The optical and the electronic response of the Ge(111)-c(2 × 8) surface to O2 exposure

This Communication describes a study concerning the interaction of molecular oxygen with a clean Ge(111)-c(2 × 8) surface. This reaction has been studied by in situ monitoring the ellipsometric reflection and the surface conductance. In order to explain the experimental results a model is proposed assuming a gradual disappearance of donor and acceptor surface states. The final stage in the adsorption process is characterized by the saturation of an acceptor surface state related to an optical transition at hv = 1.9 eV

An investigation of the interaction of N2O with the Si(111)-7 × 7 surface using AES and optical reflectometry; A comparison with O2

At 300 K, N2O decomposes into N2, leaving behind atomic oxygen at the Si(111)¿7 × 7 surface. Decomposition at two different sites is proposed, having the overall initial reaction probability: s(0) = (6.7 ± 0.7) × 106. SiOx(x not, vert, similar 1) bonds are predominantly formed, saturation occurring at monolayer coverage. This oxygen monolayer appears to completely prevent further oxygen uptake by additional N2O or O2 exposures, in contrast with the adsorption behaviour of O2 on Si(111)-7 × 7, which exhibits slow sorption beyond one monolayer

The Ti/c-Si solid state reaction : I. An ellipsometrical study

This paper is the first of a series of three articles in which we present the results and analyses of an extended study of the c-Si/Ti solid state reaction. In this paper we will discuss the spectroscopic ellipsometric investigation. Thin (≈10nm) Ti films are grown on clean Si(111) surfaces and are subsequently heated. The Si indiffusion and the Si-Ti intermixing are continuously registered by three-wavelengths ellipsometry. Two metastable intermediate phases are observed to form before the final state is obtained Spectroscopic ellipsometry (E = 2−4.5 eV) is used to characterize the as-deposited layer, the metastable intermediate phase and the final state. Analysis of these spectra shows that: (1) Si and Ti intermix during the initial Ti deposition, (2) a fast reordering of the Ti atoms occurs when the system is slightly heated (≈175°C), (3) a metastable, probably monosilicide phase with a large Si concentration gradient is obtained at ≈350°C, (4) a homogeneous metastable TiSi2 forms at ≈450°C, at ≈700°C a roughened TiSi2 layer with a surplus of c-Si is formed

A novel derivative ellipsometric method for the study of the growth of thin films: Titanium

The growth of a titanium film at room temperature from an evaporation source on a silicon substrate covered by its native oxide layer is continuously monitored with an ellipsometer at three wavelengths. The momentary positions and the derivatives of the trajectories thus obtained in the (Δ, Ψ) plane can be used for uniquely determining the momentary thickness and the momentary dielectric constants of the layer at each of the wavelengths. The optical properties of the titanium, which reflect the film structure and defect rate, strongly depend upon the growth conditions; the top region of a film approximately 40 nm thick appears to contain more voids and lattice defects than the region near the substrate

Systematic and random errors in rotating-analyzer, ellipsometry

Errors and error sources occurring in rotating-analyzer ellipsometry are discussed. From general considerations it is shown that a rotating-analyzer ellipsometer is inaccurate if applied at P = 0° and in cases when π = 0° or where Δ is near 0° or 180°. Window errors, component imperfections, azimuth errors and all other errors may, to first order, be treated independently and can subsequently be added. Explicit first-order expressions for the errors δΔ and δπ caused by windows, component imperfections, and azimuth errors are derived, showing that all of them, except the window errors, are eliminated in a two-zone measurement. Higher-order errors that are due to azimuth errors are studied numerically, revealing that they are in general less than 0.1°. Statistical errors are also discussed. Errors caused by noise and by correlated perturbations, i.e., periodic fluctuations of the light source, are also considered. Such periodic perturbations do cause random errors, especially when they have frequencies near 2ωA and 4ωA

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