Chemical and microstructural study of the oxygen passivation behaviour of nanocrystalline Mg and MgH2

Nanocrystalline Mg and MgH₂ samples have been prepared by high-energy ball milling and gas phase condensation methods. Starting from these materials in their “as received” state without air exposure, a study of the oxygen and air passivation behaviour was carried out by “in situ” analysis of the samples by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The binding energy and photoemission Auger parameters have been determined for metallic magnesium as well as for magnesium hydride, oxide and hydroxide species. Values of the MgH₂ material were reported for the first time. The study clearly shows the formation of an oxide passivation layer of ca. 3-4 nm in thickness for all the nanocrystalline magnesium samples handled under controlled inert gas atmospheres. A hydroxide like amorphous layer is formed at the topmost surface layers of the nanocrystalline Mg and MgH₂ samples. The implication of these studies for H₂ storage and transport applications of nanocrystalline magnesium is discussed.     

Analysis of mechanism of carbon removal from GaAs(1 0 0) surface by atomic hydrogen

Etching of carbon contaminations from the GaAs(1 0 0) surface by irradiating with atomic hydrogen, which is one of the key reactions to promote high-quality thin films growth by molecular beam epitaxy (MBE), has been investigated by mass spectrometry (MS), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). It is shown that during the cleaning process at room temperature a total reduction of the Auger carbon signal, accompanied by desorption of methane as major reaction product, can be observed. The reaction pathways as well as the processes responsible for the observed carbon removal are discussed in detail to give a support for etching and growth quality enhancement not only in thin films epitaxy but in all atomic hydrogen promoted gas-phase III-V semiconductor processes.     

Décomposition thermique du monoxide de carbone sur une surface de molybdène: Formation de couches superficielles de carbone et de carbure

We have investigated the decomposition of carbon monoxide on polycrystalline and (001), (110) monocrystalline molybdenum surfaces. This study was performed by massspectrometry, for thermal desorption studies, Auger electron spectrometry (AES), low energy electron diffraction (LEED) and photoelectron spectroscopy (ESCA). By heating the clean Mo surface in CO or by heating the Mo surface covered with CO, the dissociation of chemisorbed CO leads to a build-up of carbon layer which inhibits the subsequent adsorption. Two distinct types of fine structure are associated with the KLL line of carbon Auger spectra. If the Mo surface is heated at a temperature between 300 and 1500 K, the Auger peak is characteristic of a “graphite layer”. If the Mo surface is heated at a temperature up to 2000 K, the Auger peak is characteristic of a “carbure” layer. This “carbure layer” give rise to a surstructure which agrees with a Mo₂C surface layer and was also investigated by ESCA. Chemical shifts of (1s) C and (3d) Mo photoemission bands were observed and attributed to the bounding between Mo and C atoms in the Mo₂C layer.     

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.     

Chemical modification of the surface of Fe<Subscript>75</Subscript>Si<Subscript>25</Subscript> alloy particles with stearic acid under high-energy ball-milling conditions

The morphology, phase composition and surface structure of Fe₇₅Si₂₅-alloy particles are studied by electron microscopy, X-ray diffraction analysis, and Mössbauer, Auger, IR (infrared) and X-ray photoelectron spectroscopy. The alloy particles used as fillers for the polyethylene matrix are produced by high-energy ball milling in an organic medium with the addition of stearic acid. The addition of stearic acid is shown to promote plasticization of the brittle Fe₇₅Si₂₅ alloy and the formation of a surface layer of no more than 1.5 nm thick, consisting of oxides based on iron and silicon, responsible for the chemisorption of stearic acid on the surface. Chemical modification of the surface of filler particles with an amphiphilic surfactant is carried out to enhance their adhesion in the polymer matrix.     

Interfacial structure and electrical properties of LaAlO3 gate dielectric films on Si by metalorganic chemical vapor deposition

LaAlO₃ (LAO) gate dielectric films were deposited on Si substrates by low-pressure metalorganic chemical vapor deposition. The interfacial structure and composition distribution were investigated by high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), secondary-ion mass spectroscopy (SIMS), and Auger-electron spectroscopy (AES). HRTEM confirms that there exists an interfacial layer between LAO and Si in most samples. AES, SIMS, and XPS analyses indicate that the interfacial layer is compositionally graded La–Al silicate and the Al element is severely deficient close to the Si surface. Electrical properties of LAO films were evaluated. No evident difference in electrical properties between samples with and without native SiO₂ layers was observed. The electrical properties are discussed in terms of LAO growth mechanisms, in relation to the interfacial structure. PACS 73.40.Qv; 81.15.Gh; 77.55.+f; 68.35.-p     

The bonding state of carbon segregated to α-iron surfaces and on iron carbide surfaces studied by electron spectroscopy

Segregated carbon on the Fe(100) surface has been studied by means of X-rayand ultraviolet photoelectron (XPS, UPS), Auger electron (AES) and electron energy loss spectroscopy (ELS). For comparison, the surfaces of polycrystalline graphite and of iron carbides stabilized by chromium or manganese additions have been investigated. On the iron surface, carbon exists as a chemisorbed state or graphitic multilayer. The two states exhibit different energy positions in XPS, and are different in energy positions and lineshapes in AES and ELS. During the transition of graphitic carbon to chemisorbed carbon on Fe(100) a novel coverage-dependent Auger feature is reported. The spectra of graphitic carbon on the iron surface always coincide with those of solid graphite. The carbon Auger transitions of chemisorbed carbon and of iron carbides exhibit very similar lineshapes, but the energy positions of both states differ in AES as well as XPS.     

X-ray photoelectron and auger spectroscopy analysis of Ge:Mn-based magnetic semiconductor layers

Thin (～60 nm) germanium layers supersaturated with a manganese impurity of 10–16 at % have been studied by x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The layers have been fabricated by pulsed laser deposition onto a semi-insulating single-crystal GaAs substrate. The results of XPS analysis of the Ge:Mn layers reveal a change in the line shape of germanium and manganese (2p) in the surface region compared to deeper layers, which indicates a transition from the oxidized form of the base material (Ge²⁺ and Ge¹⁺) and impurity (Mn²⁺) near the surface to the unoxidized state of germanium (Ge ⁰) and manganese (Mn⁰) in the interior of the layer. The XPS spectra of the valence electrons of the Ge:Mn structure indicate that the density of states in the valence band of the ferromagnetic Ge:Mn structures is caused not only by mechanical mixing of germanium and manganese. The composition of heterogeneous inclusions in Ge:Mn films has been studied using scanning Auger microscopy.     

Surface analysis of biocompatible coatings on titanium

The coatings of hydroxyapatite, which is widely used for orthopaedic and dental prothesis, were deposited by using the dip-coating method. The layers of hydroxyapatite were grown on commercial Ti substrates. In order to improve the adhesion of hydroxyapatite, the substrate was a priori covered with titania or calcium titanate by using the sol-gel technique. For comparison, commercial samples of hydroxyapatite coating (manufactured by means of plasma-spray apparatus) were analysed. The chemical composition and the structure of the coatings (TiO₂, CaTiO₃ and hydroxyapatite) were studied by using X-ray photoelectron spectroscopy (XPS), scanning Auger microscopy (SAM), X-ray diffraction (XRD) and secondary electron microscopy (SEM) techniques. The data of quantitative XPS analysis and the surface images (SAM and SEM) displayed the superior quality (cleanness, homogeneity, etc.) of hydroxyapatite deposited by sol-gel in comparison with commercial samples investigated.     

P110钢CO2腐蚀产物膜的XPS分析

为了确定CO2腐蚀产物膜的组成及不同层次结构中成分和含量的差异,采用P110钢在高温高压腐蚀静态釜中制备CO2腐蚀产物膜,利用SEM观察了腐蚀产物膜的表面和断面形貌,结合XRD分析结果,通过XPS研究了两层结构膜的化学组成差异。结果表明,腐蚀产物膜断面呈现双层结构;膜层的主要成分是FeCO3,还有少量的CaCO3和铁的氧化物,但内层CaCO3较多且夹杂着Fe3C和单质Fe,外层氧化物稍多;通过内外层Ca^2＋含量差异推断出内层腐蚀膜优先形成。     

Formation and investigation of cobalt silicide ultrathin layers in Ti/Co/Ti-, TiN/Ti/Co-, and TiN/Co-on-silicon structures

The formation of ultrathin CoSi₂ layers in Ti(8 nm)/Co(10 nm)/Ti(5 nm), TiN(18 nm)/Ti(2 nm)/Co(8 nm), and TiN(18 nm)/Co(8 nm) systems magnetron-sputtered on the Si(100) surface is studied. The systems are subjected to two-step rapid thermal annealing. In between the annealing steps, the “sacrificial” layer is chemically removed and the second and third systems are additionally covered by a 17-nm-thick amorphous silicon (α-Si) layer. In the course of the fabrication process, the structures are examined using time-of-flight secondary-ion (cation) mass spectrometry, Auger electron spectroscopy, and scanning electron microscopy combined with X-ray energy dispersion microanalysis. It is shown that the above complex of analytical investigation provides efficient physical control of ultrathin silicide layer formation.     

Microstructure and composition of catalytic layers formed by the ion-beam-assisted deposition of platinum onto carbon substrates

The results of investigating the microstructure and composition of layers formed by platinum deposition onto carbon carriers used as electrocatalysts—MG-1 graphite, SU-2000 glassy carbon, and AVCarb® P50 carbon fiber paper—are presented. The layers have been created via the ion-beam-assisted deposition of platinum, in which metal deposition and mixing between the deposited layer and substrate-surface atoms accelerated by ions of the same metal (U = 10 kV) occur, respectively, from a neutral vapor fraction and the vacuum-arc discharge plasma of a pulsed ion source. The layers are examined via scanning electron microscopy, electron probe microanalysis, electron backscatter diffraction, Rutherford backscattering spectrometry, and X-ray photoelectron spectrometry. The formed layers (their thicknesses are ～100 nm and the platinum content is ～10¹⁶ atom cm^?2) are characterized by an amorphous atomic structure that repeats the surface microstructure of the carbon carrier.     

Thermal reaction and desorption behaviors of 2,5-diiodothiophene on clean and passivated Au surfaces

Thermal reactions and desorption behaviors of 2,5-diiodothiophene on Au were studied with temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES). Diiodo-substituted hetero-cyclic molecules are an important precursor molecule for photochemical production of conjugated polymers. This paper describes the surface reactions and multilayer structure of 2,5-diiodothiophene in the absence of photon irradiation. 2,5-Diiodothiophene adsorbs molecularly on Au at 100 K. At 200-300 K, the C-I bond of the molecule dissociates producing atomic iodine. The C-I bond cleavage appears to induce further dissociation of the thiophene ring structure. The iodine species desorb at 600-750 K from the surface. The dissociated carbon and sulfur remain on the Au surface even at 800 K. The desorption of thin multilayers occurs at ∼220 K. During the desorption of these layers, a clustering process seems to occur. The desorption of thick multilayer occurs at ∼235 K.     

Thermal decomposition of 1,1-dimethylhydrazine on Si(100)-2 × 1

The surface reaction of 1,1-dimethylhydrazine (DMH) with Si(100) has been studied with temperature programmed desorption spectroscopy (TPD), temperature programmed static secondary ion mass spectrometry (TPSSIMS), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES). Adsorption of DMH on Si(100) at 170 K followed by annealing to 1100 K results in significant decomposition to form surface carbide and nitride. TPD results show that the only gas phase desoprtion products are hydrogen and dimethylamine. Furthermore, decomposition occurs over a broad temperature range; XPS and TPSIMS results indicate C---N bond cleavage beginning at 400 K and by 600 K, all the C---N bonds have dissociated. We propose a molecular level mechanism that involves partial decomposition upon adsorption followed by extensive bond cleavage to form surface carbide and nitride.     

Mechanical properties of hexagonal boron nitride synthesized from film of Cu/BN mixture by surface segregation

Hexagonal boron nitride (h-BN) has a low friction coefficient and weak surface attractive force similar to graphite. Furthermore, while graphite is conductive, BN is a good insulator. These properties make it suitable for application like lubricating coating or as an insulator/buffer layer in electronic devices. The synthesize of h-BN layer by surface segregation phenomena and mechanical properties of the h-BN surface segregated on Cu substrate have been investigated. During in situ annealing, the surface segregation of BN occurred on Cu/BN film deposited by deposition process with a rf magnetron co-sputtering system. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) analysis showed that though the h-BN layer synthesized was not covered whole area of substrate but the h-BN layers partially covered substrate. And the concentration of oxygen on the surface after exposure in air is decreased with increase of BN concentration. The topography of atomic forces microscopy (AFM) showed that h-BN phases surface segregated are discontinuous droplet shape. The force curves of AFM and friction force of lateral force microscopy (LFM) showed that the h-BN droplet surface segregated have very weak attractive force and low friction coefficient equal to h-BN sintered plate.     

原子层沉积方法制备核-壳型纳米材料研究

采用原子层沉积方法在碳黑纳米颗粒表面分别沉积Al₂O₃, ZnO, TiO₂和Pt, 成功制备出核-壳型纳米材料. 通过高分辨率透射电子显微镜、X射线光电子能谱仪、 能谱仪对材料的表面形貌、晶体结构、薄膜成分进行了表征和分析. 结果表明, 原子层沉积方法是制备核壳型纳米材料的理想方法. 此外, 还分析了采用原子层沉积方法沉积不同材料, 所生长的薄膜材料有单晶、多晶、非晶等多种存在形式的形成原因. 关键词： 原子层沉积 核-壳型纳米材料 碳黑纳米颗粒     

Study on the bonding state for carbon-boron nitrogen with different ball milling time

The varied bonding state and microstructure characterization were discussed for carbon-boron nitrogen (CBN) with abundant phase structure and nanostructure, which were synthesized directly by mechanical alloying technique at room temperature. According to the results of SEM and X-ray photoelectron spectroscopy (XPS) of CBN with different ball milling time, it is substantiated that the bonding state and microstructure for CBN were closely related to the ball milling time. With the increase of the ball milling time, some new chemical bonding states of CBN were observed, which implies that some new bonding state and microstructures have been formed. The results of XPS are accordance with that of X-ray diffraction of CBN.     

High-temperature oxidation of CrN/AlN multilayer coatings

Experiments are reported on sputter depth profiling of CrN/AlN multilayer abrasive coatings by secondary ion mass spectrometry (SIMS) coupled with sample current measurements (SCM). The coatings were deposited by a closed-field unbalanced magnetron sputtering. It is shown that after oxidation tests, performed in air at 900 °C for 2 h and at 1100 °C for 4 h, the layered structure begins to degrade but is not destroyed completely. Oxidation at 1100 °C for 20 h causes total destruction of the coatings that can be attributed to a fast diffusion of oxygen, nickel, manganese and other elements along defect paths (grain boundaries, dislocations, etc.) in the coating. There are practically no nitrides in the near-surface layer after such a treatment and all the metallic components are in the oxidized form as follows from the data obtained by X-ray photoelectron spectroscopy (XPS). According to XPS and mass-resolved ion scattering spectrometry (MARISS), the surface content of Al in the heat-treated coatings has decreased in comparison with the as-received sample and that of Cr increased. Both XPS and MARISS data exhibit real increase in superficial concentration of the substrate materials (Mn and Ni) that is controversial if using SIMS alone. SCM turned out to be an informative depth profiling method complementary to more expensive and complicated SIMS, being particularly useful for structures with different secondary electron emission properties of the layers. SCM with predetermined SIMS calibration allows a routine characterization of coatings and other multilayer structures, particularly, in situations where the expenses of analysis can be justified.     

The Effect of Triethylene-Tetramine Treatment of Carbon Fibers on Performance of Composites

Amino groups can be introduced to the surface of carbon fibers (CF) by triethylene-tetramine (TETA) treatment. Carbon fibers coated with triethylene-tetramine (TETA) were treated at 400°C for 30 s in an oxidizing furnace. Differential scanning calorimetry studies showed that the surface functional groups of CF reacted with TETA. The changes of the surface composition and structure of CF were tested by X-ray photoelectron spectrometry (XPS). The interfacial interaction between the resulting CF and an epoxy matrix was also characterized by scanning electron microscopy (SEM) and three-point short-beam shear testing. The XPS results indicate that the number of amino groups on the surface of the CF was significantly increased after being treated with TETA. The interlaminar shear strength (ILSS) of TETA-treated CF-reinforced resin composites (CFRP) was increased by 30% compared with untreated ones, and in the treated CF fracture sections, CFRP pores and carbon fiber pullout were seldom observed. The failure of composites reinforced by treated CF shows a cohesive failure effect in the interface layer.     

Gd adsorption on the Mo(2 1 1) surface

The adsorption of Gd thin layers on the Mo(2 1 1) face was investigated by using Auger electron spectroscopy (AES), low electron energy diffraction (LEED), scanning tunneling microscopy (STM), X-ray photoemission spectroscopy (XPS) and measurements of the work function changes (Δφ). It was found that at 300 K Gd does not form any dilute chain structures and from the very beginning of the adsorption process Gd forms a densely packed layer. The dilute p(4 × 1) chain structure was observed by LEED after annealing thin layers (θ < 1 ML) to temperatures above 770 K. STM images confirm the existence of the p(4 × 1) structure islands. The intermixing of the substrate and adsorbate atoms takes place.