Decomposition of N2O on the Si(100)2 × 1 and Si(111)7 × 7 surfaces: Determination of the density of broken bonds

This paper reports on the site-specific decomposition behaviour of N2O onthe clean Si(100)2 × 1 and Si(111)7 × 7 surfaces at room temperature, studied by spectroscopic differential reflectometry (SDR) and Auger electron spectroscopy (AES). It has been established that Si---O bond formation occurs at the toplayer Si atoms, mainly via attachment of the unsaturated broken bonds. In this way it is possible to determine the density of broken (dangling) bonds at the clean Si surface. Our results confirm the high dangling bond density at the 2 × 1 reconstructed Si(100) surface for which we assume a defect density of 15 ± 10%. The density of dangling bonds per 7 × 7 unit cell (49 atoms), 23 ± 4, is in agreement with the established 19 as revealed by current imaging tunneling spectroscopy (CITS)

The adsorption behaviour of O2 on the clean Si(110) surface in the early stage

This Letter reports on the early stage of adsorption of O2 on the clean Si(110) surface, showing a prominent 5×1 reconstruction, in ultrahigh vacuum at 300 K. Auger electron spectroscopy (AES) and low energy electron diffraction (LEED) have been used to monitor this solid-gas reaction. Careful measurements of the normalized oxygen Auger signal in the low exposure region reveal, for the first time, a remarkably fast adsorption of O2 up to 0.15 monolayer of oxygen, the initial sticking probability being about 1. The LEED measurements suggest that those surface sites which constitute the additional higher order reconstructions, are highly reactive

Kinetics of the adsorption of atomic oxygen (N2O) on the Si(001)2x1 surface as revealed by the change in the surface conductance

The adsorption behaviour of N2O on the Si(001)2 × 1 surface at 300 K substrate temperature has been investigated by measuring in situ the surface conductance during the reaction process. For comparison we monitored in the same way the adsorption of O2 on the same surface which ultimately leads to the flat band situation. The adsorption of atomic oxygen as released by decomposition of the N2O molecule, in contrast with molecular oxygen, was found to result in an increase of the band bending. The difference in behaviour of the change of the surface conductance between the two solid-gas reactions can be explained by considering that the adsorption of O2 will also remove deep-lying backbond states in addition to the dangling bond (DB) and dimer bond (DM) related surface states. It is well known that only the DB and DM surface states are affected by N2O. The surface conductance measurements (SCM) presented in this paper complement our previous spectroscopic differential reflectivity measurements and Auger electron spectroscopic results for the system Si(001)2 × 1 + N2O; we have found evidence that the second step of the proposed three-stage adsorption process of atomic oxygen can be divided into two substages. From our SCM data we could derive that the distance between the valence band edge and the Fermi energy of the clean Si(001)2 × 1 surface is 0.32 ± 0.02 eV, which is in agreement with previous photoemission results

The influence of inter-atomic transitions in Auger valence band spectroscopy: oxygen on Si(001)2x1

In this paper we will show that the description of an Auger process in terms of a process confined to one atom is in general not adequate and the Mulliken population is only in very specific cases a good alternative in evaluating the strength of inter-atomic transitions. The ionicity of the chemical bond cannot be used as a direct measure of the contribution of inter-atomic Auger transitions, as will be demonstrated in the case of the oxygen KVV Auger transitions in gaseous molecular oxygen and oxygen chemisorbed on the Si(001) surface. A full evaluation of inter-atomic transition rates shows that their strength depends on the inter-atomic distance as well as on the screening of the initial core hole

The Ti/c-Si solid state reaction, II. additional measurements by means of RBS and AES

In a previous paper [Appl. Surface Sci. 40 (1990) 333], we have reported the results of a spectroscopic ellipsometric study of the c-Si/Ti solid state reaction. For this purpose we have grown and heated thin (≈10nm) Ti films on a clean c-Si substrate. The investigation revealed that already at moderate temperatures a metastable silicide (≈350°C), probably a monosilicide, and disilicide (≈450°C) are formed. These two metastable transition states, denoted by state I and II respectively, and the final disilicide (state III, ≈700°C) are additionally studied by means of a number of quantitative techniques, such as RBS, XPS and AES. The results reveal a Si-enriched monosilicide state I, Si: Ti = 1.2 and a stoichiometric but Si segregated disilicide state II; surface composition approximately TiSi3. The finally obtained disilicide (III) has recrystallized into probably large, flat islands embedded in a c-Si matrix

Composition and thickness of surface layer on molybdenum tips for scanning tunnelling microscopy (STM) studied by SEM/AES/(AR)XPS

A combination of SEM, AES and angle-resolved XPS (ARXPS) has been applied to analyse the distribution of chemical compounds in the surface region of electrochemically etched molybdenum tips and to determine the contamination layer thickness. Carbon monoxide, graphite, molybdenum carbide and molybdenum oxide were found to be the main surface contaminants on molybdenum tips. Auger line profiling revealed a significant enrichment of carbon and oxygen upon the tip. The thickness of the oxygen-carbon contamination layer on the tip was estimated to be 13.5 ± 1.0 nm as measured by AES. The thickness of the contamination layer on a molybdenum sheet was found to be 8.0 ± 1.5 and 6.8 nm using AES and ARXPS respectively. Quantitative analysis of the surface concentrations of carbon, oxygen and molybdenum has been performed

Adsorption of atomic and molecular oxygen on Si(100)2x1: coverage dependence of the Auger O KVV lineshape.

By means of Auger electron spectroscopy (AES) we have monitored the room temperature adsorption of O2 and N2O on the clean Si(0 0 1)2 × 1 surface. We have found, for the first time, a significant variation in the intensity ratio of the K L1 L1 and K L23 L23 O Auger lines in the submonolayer range. This variation can be related to a change in bonding configuration of the oxygen atom/molecule in the initial adsorption stage in which the influence of inter-atomic matrix elements of the Auger process cannot be neglected

Distribution and thickness of the surface contaminations on STM tungsten tips, studied by AES/SEM and ARXPS

The combination of Auger electron spectroscopy (AES), scanning electron microscopy (SEM) and angle resolved X-ray photoelectron spectroscopy (ARXPS) has been applied to the analysis of the distribution of elements at the surface region of electrochemically etched tungsten tips and the determination of the thickness of a layer with oxygen and carbon contamination. Auger line profiling revealed a homogeneous distribution of oxygen and significant enrichment of carbon on the W tip between 0 and 1.5 μm from the top. The thickness of the contamination layer on various W materials, electrochemically etched, was found to be 1.35±0.15 nm as measured using ARXPS, and was estimated to be about 1–3 nm as measured by AES