Angle-resolved X-ray Photoelectron Research Articles

Adsorption of silicon atoms on the surface of the Au/W(110)

The possibility of formation of an ordered silicene-like structure on Au/W(110) surface has been considered using angle-resolved photoelectron spectroscopy and X-ray photoelectron spectroscopy. It is shown that the addition of silicon atoms results in a considerable distortion of the electron structure of the initial substrate, and the resulting electron structure cannot be attributed to silicene. The configuration of reflections in the low energy electron diffraction pattern indicates the formation of two-dimensional ordered silicon structures with a large number of multidirectional domains.

A study of the transition of liquid-crystal alignment from homeotropic to planar on a polyimide layer

The alignment of nematic liquid crystals by rubbed polyimide surfaces has been well-studied and developed. A novel polyimide film which induced a homeotropic alignment of the nematic liquid crystal without rubbing or with weak rubbing strength was presented. However, there was a transition from homeotropic to planar alignment of the nematic liquid crystal after strong rubbing. In order to study the transition, the polyimide surface was investigated by atomic force microscopy, surface free energy measurement and angle-resolved analysis X-ray photo-electron spectroscopy before and after rubbing with a velvet fabric. It was found that both the change of surface polarity and surface morphology were not the reasons for the transition. The droop of the side chain on the polyimide surface after the rubbing treatment was detected by angle-resolved analysis X-ray photo-electron spectroscopy. Owing to the special structure of the novel polyimide, the X-ray photo-electron spectroscopy was successfully used for the first time to analyse the conformational change of the side chain of a polymer. In conclusion, the transition of nematic liquid crystal alignment from homeotropic to planar after rubbing was influenced by the side chain conformation of the polyimide.

Process-Structure Relationships of Nitrided Oxides and Oxynitrides

AbstractThe presence of nitrogen in the dielectric films is known to impart highly desirable properties in the ultra-large-scale-integration era; the position, amount and concentration profiles of nitrogen are therefore of great interest. In this work, we investigate two-step processes leading to bimodal nitrogen profiles, with one nitrogen peak near the Si/dielectric interface and the other near the dielectric surface. At 1000°C and 1 atm, a nitridation step with NH3 following either an oxidation (in O2) or oxynitridation (in N2O) step is found to result in a bimodal nitrogen concentration profile for short nitridation times. Increasing the duration of the nitridation step with NH3 is found to completely nitridate the entire film. Secondary Ion Mass, Angle Resolved X-Ray Photoelectron, and Fourier Transform Infrared Spectroscopic studies are shown to support these observations. Therefore, based on such process-property-structure relationships, the engineering of desired nitrogen concentration profiles in nano-dielectric materials of interest becomes possible. Such knowledge may have significant implications on micro- and nano-electronic applications of silicon oxynitrides.

Atomic Scale Nitridation of Silicon Oxide Surfaces by Remote-Plasma-Excited Nitrogen

ABSTRACTWe have incorporated several percent of nitrogen only near the top surfaces of thermally grown oxides by exposure to fluorine gas at room temperature followed by an atomic nitrogen treatment at 550°C. The depth profiles and the bonding of incorporated nitrogen atoms have been studied by angle-resolved x-ray photoelectron spectroscopy.MOS devices were fabricated using the nitrided oxide with boron doped polycrystalline silicon gate. From the capacitance-voltage measurements we confirmed that the nitrided oxide would prevent the boron penetration in comparison with the conventional oxide films. The proposed technique identifies a unique process for obtaining high quality ultrathin dielectrics.

SiO2/Si(100)model support with AES and XPS in combination with MLCFA

Model supports consisting of a thin layer of SiO2 on a silicon single crystal offer tremendous advantages for the study of heterogeneous catalysts. Using model supports, the use of angle-resolved and depth profiling X-ray photoelectron spectroscopy has now become meaningful. The Varimax Promax transformation (VPT) technique for maximum likelihood common factor analysis (MLCFA) has been proposed as an alternative method to the traditional transformations. The so-called VPT technique makes no use of spectral reference libraries. Both MLCFA and VPT are incorporated in a factor analysis software package which has been applied, in combination with XPS and AES, to the study of thin layers of SiO2 on Si(100).

Adsorption of self-assembled monolayers of mercaptan on gold.

XPS and AES are suitable techniques for studying organic monolayers on metals if radiation doses are kept low. The adsorption of self-assembled (SA) mercaptan monolayers on gold is a process in two stages. The adsorption to near completeness is very rapid. However, the process of orientation of the carbon chains, which is responsible for the blocking of electrochemical reactions takes much longer, as could be shown by ARXPS (angle resolved X-ray photo electron spectroscopy). Adsorption under potential control allows electrochemical experiments during the adsorption process as e.g. the measurement of the capacity of the electric double layer. Furthermore the control of the potential guarantees sure that the metal/liquid interface is well defined during the adsorption process.

A study of polar CdTe (111) surfaces using angle-resolved x-ray photoelectron and Auger electron spectroscopy and low-energy electron diffraction

X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and low-energy electron diffraction (LEED) have been used to study the polar (111)Cd and (111)Te surfaces of intrinsic CdTe crystals. Complementary information on surface composition, chemical state of the surface elements, and surface structure was obtained. The Auger parameters were used to identify the chemical states of elements on surfaces of semi-insulating undoped CdTe crystals which suffered from static charging effects. With this approach, we were able to determine that after chem-mechanical polishing, the Te-rich surface layer was mostly in the pure Te state. Only a trace amount of TeO2 was detectable. Sputtered and vacuum annealed (111) surfaces were found to be stoichiometric: both Cd and Te were in the chemical state of CdTe. Both (111) Cd and (111) Te surfaces showed sixfold symmetric LEED patterns. No evidence of surface reconstruction was found. Angle-resolved XPS showed no significant difference between 0° and 70° tilt on either the (111) Cd or (111) Te surfaces. Angle-resolved AES, however, showed significant differences between (111) Cd and (111) Te at 0° and 70° tilt, and the crystallographic polarity identified this way was consistent with results based on chemical etching and standard AES techniques, and with reported results of x-ray diffraction and transmission electron microscopy.

The effect of carbonaceous contamination on the investigation of the surface oxide on silicon by angle-resolved XPS

The carbon-contaminated native oxide layer on a standard silicon wafer was investigated by angle-resolved signal ratio X-ray photoelectron spectroscopy (AR/SR/XPS). The results, based on intensity measurements of C1s , O1s , Si 2 4+ and Sielemental 2p showed the carbon to be “ingested” into the oxide to a mean depth of 0.4 nm, and the oxide to consist of a fully oxidized layer (∼ 1 nm) on top, followed by a suboxidic layer (0.8 nm). The conclusions are that the depth location of the carbonaceous contamination is of cardinal importance for the correct interpretation of the oxidic data, and that for well studied systems routine measurements at two take-off angles suffice for quantitative results.

An analysis of angular dependent XPS peak intensities

Angle resolved X-ray photoelectron (XPS) studies of clean Ni(100) and of exitaxial Cu and Co films on Ni(100) have been interpreted with the aid of single scattering cluster calculations. It is found that for atoms in the top few atomic layers, photoelectron forward scattering by overlying atoms in the lattice causes XPS peak intensities to be enhanced at angles corresponding to nearest neighbor and next-nearest neighbor internuclear axes. Angle resolved XPS should thus be an excellent approach for gaining structural information on, for example, epitaxial overlayers or surface reconstructions.