The role of nitrogen in the preferential chromium segregation on the ferritic stainless steel (1 1 1) surface

The temperature dependence on the segregation behavior of the ferritic stainless steel single crystal (1 1 1) surface morphology has been examined by scanning tunneling microscopy (STM), Auger electron spectroscopy (AES), and low energy electron diffraction (LEED). AES clearly showed the surface segregations of chromium and nitrogen upon annealing. Nanoscale triangular chromium nitride clusters were formed around 650 °C and were regularly aligned in a hexagonal configuration. In contrast, for the ferritic stainless steel (1 1 1) surface with low-nitrogen content, chromium and carbon were found to segregate on the surface upon annealing and Auger spectra of carbon displayed the characteristic carbide peak. For the low-nitrogen surface, LEED identified a facetted surface with (2 × 2) superstructure at 650 °C. High-resolution STM identified a chromium carbide film with segregated carbon atoms randomly located on the surface. The facetted (2 × 2) superstructure changed into a (3 × 3) superstructure with no faceting upon annealing at 750 °C. Also, segregated sulfur seems to contribute to the reconstruction or interfacial relaxation between the ferritic stainless steel (1 1 1) substrate and chromium carbide film.     

Interface structures and rotational epitaxy of titanium on tungsten (110)

Interface structures of ultrathin Ti films grown on W(110) have been studied by low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) in a wide range of annealing temperatures. The interface structures observed are interpreted to be due to site-coincidence growth (commensurate growth) and rotational epitaxy (incommensurate growth), respectively. The first monolayer of titanium is very strained with a large unit-cell expansion of 12.7% relative to that of Ti(0001). Deposition of additional Ti atoms destroys the strained structure, leading to rotational epitaxy: two Ti(0001) domains rotating mutually by 9.9 °. A thermally stable Ti bilayer exists at high annealing temperatures.     

Effect of impurities on the surface morphology of Fe(111)

The surface composition and morphology of Fe(111) have been examined through a combined analysis that includes low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and scanning tunneling microscopy (STM). The preferential segregation of sulfur has been clearly identified by AES upon annealing. The STM images exhibit numerous triangular pits of various sizes, and the LEED patterns show diffused n × 1 spots. The triangular pits reveal a Sierpinski gasket fractal. For sulfur-free Fe(111), nitrogen segregates to the surface upon annealing, forming a 4√3 × 4√3 superstructure that is identified by LEED patterns and STM images. The STM images show nanoscale triangular clusters regularly aligned in a hexagonal 4√3 × 4√3 configuration. Ultra-thin chromium film deposited on a nitrogen-segregated Fe(111) surface with post-annealing induces further nitrogen segregation, resulting in the formation of triangular pyramid-shaped CrN nanoclusters.     

Amorphous SiC film formation on Si(100) using electron beam excitation

The effect of electron impact on methylsilane (CH₃SiH₃) conversion to amorphous-Si_0.5C_0.5:H (a-Si_0.5C_0.5:H) films on Si(100) has been studied by Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption (TPD), and low energy electron diffraction (LEED). It is found that electron impact greatly enhances CH₃SiH₃ decomposition on Si(100) at both 90 K and 300 K, resulting in a-Si_0.5C_0.5:H thin film formation. Thermal annealing of the film causes hydrogen desorption and amorphous silicon carbide (a-SiC) formation. Upon annealing to temperatures above 1200 K, the a-SiC film became covered by a thin silicon layer as indicated by AES studies. Ordered structures are not produced by annealing the a-SiC up to 1300 K.     

Irreversible structure transitions in Gd monolayers on Mo(112)

Low-energy electron diffraction (LEED), Auger electron spectroscopy (AES) and contact potential difference (CPD) methods have been used to investigate the structure of Gd monolayers deposited on Mo(112) at T = 78 K and the changes upon annealing in a wide temperature range, up to the beginning of desorption. In the submonolayer coverage range (θ < 0.67), the film structures p(1.3×1) and p(2×1) already formed at T = 78 K, testifying that Gd adatoms possess some mobility at rather low temperatures. The p(1.3×1) structure was found to appear at 0.07 < θ < 0.25, but it irreversibly turned into the p(2×1) structure when the annealing temperature, T_an, exceeded 500 K. Above θ = 0.25, the p(2×1) structure emerged immediately at 78 K. Formation of step arrays was observed in the range of T_an = 500–1200 K and is attributed to surface alloying. The suggestion of surface alloying is corroborated by data on annealing induced variations of the work function and Auger peak of Gd. In the coverage range 0.5 < θ < 0.67, the phase p(2×1) was found to coexist with the phase c(1.5×2), which corresponds to a physical monolayer. No evidence of surface alloy in the complete monolayer was revealed. Distinction between ordering scenarios for the systems Gd/Mo(1 1 2) and Dy/Mo(112) is discussed.     

硫在镍(100)表面偏析动力学研究

本文使用AES-LEED联合装置研究了650—800℃温度范围内硫在镍(100)表面上的偏析动力学。结果表明,在较短退火时间内硫的表面浓度正比于退火时间的平方根,与McLean的动力学模型是一致的。扩散系数与温度的关系为D(cm²/s)=5×10^-3exp(-44600/RT)。硫偏析在镍(100)表面达到饱和值,LEED观察指出形成了硫的c(2×2)结构。深度剖面分析,硫/镍俄歇峰高比随氩离子剥离时间指数降低。 关键词：     

Surface science studies of cobalt overlayers on clean and sulfur covered Mo(100) single crystal surfaces

The interaction of cobalt with clean and sulfur covered Mo(100) surfaces was investigated with Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and temperature programmed desorption (TPD). On the clean surface, the deposition and subsequent annealing of one monolayer of cobalt resulted in the formation of an ordered overlayer with (1 × 1) surface structure. When cobalt was deposited on sulfur covered Mo(100) surfaces, after annealing the sulfur overlayer migrated on top of the cobalt layer. This topmost sulfur overlayer did not significantly affect the thermal desorption of cobalt from the Mo(100) surface. Various ordered structures of sulfur, cobalt and coadsorbed sulfur and cobalt were observed by LEED. A new surface structure showing (3 × 1) symmetry was observed when at least one monolayer of cobalt was deposited and annealed at 870 K on an ordered monolayer of sulfur on the Mo(100) surface. This surface structure was stable in ultrahigh vacuum up to 940 K.     

The interaction of H2S with Si(111) 7 × 7 surfaces by energy loss and Auger electron spectroscopies

Low energy electron loss spectroscopy (ELS) and Auger electron spectroscopy (AES) have been applied for the studies of the interaction of H₂S molecules with Si(111)7 × 7 surfaces. The observations are consistent with the interpretation that the room temperature non-dissociative adsorption state of H₂S molecules changes substantially after annealing at 550°C, resulting in the desorption of hydrogen and the covalent bond formation between silicon and sulfur atoms. The silicon disulfide films formed on Si(111) surfaces have been identified by the characteristic loss peaks in comparison with those of silicon dioxide.     

Surface superstructures of the Pb/Si(001) system

In the present work the Pb/Si(001) system has been studied with LEED (low-energy electron diffraction), AES (Auger electron spectroscopy), and EELS (electron energy loss spectroscopy). Five different surface superstructures, i.e., the 2 × 2, c(4 × 8), 4 × 1, 2 × 1 and c(4 × 4) were observed. Four of them are found for the first time, except for the 2 × 1. Their relationship has been investigated as a function of Pb coverage and annealing temperature. As a result, a complete phase diagram of the system has been determined. Upon annealing at 450°C the 2 × 2 superstructure undergoes an irreversible phase transformation to the c(4 × 8), while the c(4 × 4) reversibly transforms to 2 × 1 at 300°C. Strong influence of oxygen contamination on the surface superstructures has been observed.     

Competitive segregation of impurities on the surface of polycrystalline copper

The competitive segregation of sulfur, carbon, and phosphorus on the surface of polycrystalline copper and the segregation kinetics of sulfur in the temperature range 675–875 K have been investigated by Auger electron spectroscopy. The equilibrium segregation energies of impurities and the sulfur diffusion parameters in the near-surface region of copper with a thickness d ≤ 5 μm have been calculated on the basis of the experimental data.     

Auger electron spectroscopic study of CO2 adsorption on Zircaloy-4 surfaces

We investigate the adsorption of CO₂ onto Zircaloy-4 (Zry-4) surfaces at 150, 300 and 600 K using Auger electron spectroscopy (AES). Following CO₂ adsorption at 150 K the graphitic form of carbon is detected, whereas upon chemisorption at 300 and 600 K we detect the carbidic phase. As the adsorption temperature is increased, the carbon Auger signal increases, whereas the oxygen signal decreases. Adsorption at all three temperatures results in a shift of the Zr Auger features, indicating surface oxidation. The effect of adsorbed CO₂ on the Zr(MVV) and Zr(MNV) transitions depends on adsorption temperature and is less pronounced at higher temperatures. On the other hand, changes in the Zr(MNN) feature are similar for all three adsorption temperatures. The changes in the Zr Auger peak shapes and positions are attributed to oxygen from dissociated CO₂, with the differences observed at various temperatures indicative of the diffusion of oxygen into the subsurface region.     

Surface termination of the NdGaO3(1 1 0)

Auger electron spectroscopy using excitation via grazing impact of protons was applied to determine the elemental composition of the topmost and near-surface layers of a NdGaO₃(1 1 0) substrate. The preparation conditions of vicinal NdGaO₃ substrates were optimized by varying the annealing temperature, time, and gas atmosphere. Well prepared surfaces show regularly arranged, atomically smooth terraces with single-atomic steps. The surfaces were always NdO terminated with a small amount of Ga (2-4%) atoms on the surface. A Ga and O depletion layer with a thickness of about 4 nm has been detected at optimized preparation conditions.     

An AES study of surface segregation of AgAu alloys with ion bombardment and annealing

Equilibrium segregation and selective sputtering in the surface of AgAu alloys have been investigated systematically with argon ion bombardment and with annealing by means of AES measurements. Slight enrichment of Ag was observed on the alloy surfaces after the annealing of the alloys at 550°C, while relatively large enrichment of Au was observed on the ion-bombarded surfaces with the use of Au (240 eV) and Ag (300 eV) Auger electrons. With the aid of other Auger electrons with different escape lengths, it was found that the concentration varies with distance from the surface within the sampling depth of the Auger electrons. On the basis of the above facts, the depth profiles were proposed for the annealed and the ion-bombarded surfaces. The uppermost surface layer is enriched more with Ag than the apparent AES observations on both the ion-bombarded and the annealed surfaces. The proposed depth profiles on both the surface layers were compared with previous results by different authors.     

Metallization of the Ge(111) surface at high-temperature probed by energy-loss and Auger spectroscopies

We present new electron energy-loss spectroscopy (EELS) and Auger (AES) experiments aimed to study the structural transition of the Ge(111) surface taking place at high temperatures. Our advanced high-temperature set-up allowed us to collect accurate EELS spectra near the M_2,3 excitation edges and AES MMV and MVV spectra, corresponding to different probing depths ranging from 4 to 10 Å. The metallization of the surface has been clearly detected by the shift of the M_2,3 edge and of the MMV, MVV Auger energies. A detailed study of the transition has been performed using a fine temperature step under thermal equilibrium conditions. The AES and EELS experiments show that a sudden semiconductor-metal transition takes place at about 1000 K involving mainly the topmost layers. Deeper layers within 10 Å are also involved in the metallization process (in a range of 10 above 1010 K) and a smooth change in the topmost layers is also observed at higher temperatures up to 1070 K. These transitions are not fully reversible upon cooling (down to 870 K). Structural and electronic characteristics of the surface transition are discussed in light of available models.     

Adsorption of CO on,and S poisoning of,a perfect Ni(111) single crystal and a Ni(111) crystal with small angle boundaries

A Ni(111) crystal with small angle boundaries was used to examine the adsorption of CO. The adsorption of CO on a perfect Ni(111) single crystal was used for reference. Auger spectra show that the boundary lines on the sample surface provide favorable sites for the adsorbed CO to dissociate at temperatures as low as 25°C. The post-dissociation carbon appears mostly in the form of a nickel carbide on the surface. After heating the crystal to 850°C, sulfur diffused to the surface and blocked the surface adsorption sites uniformly. The boundary-enhanced dissociation of absorbed CO is no longer observed after the diffusion of sulfur to the crystal surface. AES depth profiling of sulfur concentration at different positions on the crystal with respect to the boundary lines show no evidence that the boundary lines provide an enhanced path for sulfur diffusion.     

Auger electron spectroscopy study on the Cr/Al2O3 interfacial reactions

Interfacial reactions of evaporated chromium with surface has been studied using Auger electron spectroscopy (AES). The results reveal that the interfacial region consists of a mixture, which is a double oxide of Cr and Al or two separated oxides. After annealing, the chromium oxide and the metallic Al produced by reduction of the Al³⁺ ions were easily detected by AES at the interface. We suggest that the interfacial reaction occurs mainly by the charge transfer from the 3d electrons of Cr atoms to O 2p orbitals of the Al₂O₃ substrate. The annealing at higher temperature (973 K) is favourable to promote the interfacial reaction between the surface oxygen and the initial few atomic monolayers of the deposited chromium. The results also showed that the change of the relative Auger peak-to-peak height (APPH(%)) of the Cr LMM group peaks can be used as an index to identify the oxidation states of chromium at the Cr/Al₂O₃ interface.     

Thermally stimulated surface segregation in sodium chloride crystals

Abstract-Using the methods of X-ray microanalysis (XRMA), Auger electron spectroscopy (AES), highresolution scanning electron microscopy (HRSEM), atomic-force microscopy (AFM), IR specular reflection spectrometry (IRSRS), and quadrupole mass-spectrometry (QMS), the chemical and phase composition, as well as the morphology of the cleaved surfaces of sodium chloride crystals formed as a result of thermally stimulated surface autosegregation (TSAS), is studied. A super-stoichiometric increase in the sodium content in the surface nanolayers with an increase in temperature up to 600 K and a decrease in this content upon further heating is established experimentally. A decrease in the sodium content in the nanolayers virtually in the entire range of annealing temperatures for the reversible segregation process, as well as a decrease in this content on the surface with increasing annealing time under conditions of medium vacuum, is also been found. In addition, we observe the selective sublimation of sodium in the nanolayers at temperatures above 400 K and in the microlayers at temperatures above 600 K.     

Quantitative aspects of Auger electron spectroscopy; On the importance of attenuation of the primary electron beam

Measurements of Auger electron currents at different energies of the primary electrons and at different angles of incidence suggest that attenuation of the primary electron beam in the crystal has a significant influence on the measured Auger currents. This makes it possible to distinguish between a monolayer and a multilayer system, i.e. between impurity atoms in the top atomic layer and impurity atoms dispersed through the surface region. Comparison of AES and ellipsometric measurements of monolayer and multilayer systems on silicon and germanium surfaces shows that AES results can be interpreted to give quantitative information about the number of atoms of the type investigated.     

Origins of interdiffusion, crystallization and layer exchange in crystalline Al/amorphous Si layer systems

Aluminium-induced crystallization of amorphous silicon (a-Si) in Al/a-Si and a-Si/Al bilayers was studied upon annealing at low temperatures between 165 and 250 °C, by X-ray diffraction (XRD) and Auger electron spectroscopy (AES). Upon annealing the inward diffusion of Si along grain boundaries in Al takes place, followed by crystallization of this diffused Si. Continuous annealing leads to (more or less) layer exchange in both types of bilayers. The change in bulk energy of the Al phase (release of macrostress and microstrain, increase of grain size) promotes the occurrence of layer exchange, whereas changes in surface and interface energies counteract the layer exchange.     

Growth and alloy formation of ultrathin Ni films on Co/Pt(1 1 1)

Low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES) were used to study the growth and the structural evolution of Ni/Co/Pt(1 1 1) following high-temperature annealing. From the oscillation of the specular beam of the LEED and Auger uptake curve, we concluded that the growth mode of thin Ni films on 1 ML Co/Pt(1 1 1) is at least 2 ML layer-by-layer growth before three-dimensional island growth begins. The alloy formation of Ni/1 ML Co/Pt(1 1 1) was analyzed by AES. The temperature for the intermixing of Ni and Co layers in the upper interface without diffusing into the bulk of Pt is independent of the thickness of Ni when a Co buffer is one atomic monolayer. After the temperature was increased, formations of Ni-Co-Pt alloy, Ni-Pt alloy and Co-Pt alloy were observed. The temperature required for the Ni-Co intermixing layer to diffuse into Pt bulk increases with the thickness of Ni. The interlayer distance as a function of annealing temperature for 1 ML Ni/1 ML Co/Pt(1 1 1) was calculated from the I-V LEED. The evolution of LEED patterns was also observed at different annealing temperatures.