S.O. Saied

Surface characterisation of plasma-nitrided titanium: an XPS study

DC plasma nitriding was applied to titanium metal sheets in a commercial cell using Ar + NH3 as the admixture and the nitrided surface investigated by means of XPS. As a comparison, in situ nitriding of a chemically pure Ti surface at room temperature was performed by N2+ ion bombardment (1–5 keV) in the electron spectrometer. Synthesis of the complex Ti2p envelope was accomplished using two sets of loss peaks, separated by 1.6 and 3.0 eV from the major TiN-type Ti2p32 and Ti2p12 components. A doublet at 458.8 and 464.5 eV was also included to account for a TiO2-type oxide. The sum of the main Ti TiN peak and the two loss peaks were taken to be representative of nearly stoichiometric TiNx with x ranging from 0.85 to 1.15. Further components derived from the peak synthesis were assigned to TiNxOy and Ti2O3. The stoichiometric nitride is represented by a Ti2p doublet at binding energies of 454.7 and 460.6 eV and a single sharp N 1s peak at 396.7 ± 0.1 eV. On the superstoichiometric samples, especially after N2+ bombardment, a second peak appears at about 395.8 eV with a positive correlation between this peak concentration and the relative amounts of species (TiNxOy, Ti2O3, TiO2) derived from Ti2p components and the surface O and N content. Consecutive Ar+, N2+ and (N2+ + O2+) bombardment leads to significant changes in composition together with rearrangement of short-range chemical structure which is reflected in peak-shape changes of the Ti2p and N 1s lines.

An X-ray photoelectron spectroscopy study of the oxides of GaAs

Abstract In this paper, by the use of X-ray photoelectron spectroscopy, we unequivocally identify the oxides present on GaAs surfaces and accurately measure the binding energies associated with the 2p 3/2 , 3d, and Auger lines in the X-ray photoemission spectra. These measurements intended to provide reliable reference data for further work. We conducted an extensive analysis of the oxidation states of Ga metal and oxide powder reference samples, air exposed GaAs wafers, and wafers subjected to various surface treatments (argon plasma treatments and boiling). Based on this experimental evidence, an assignment of the photoelectron peaks to various chemical states is proposed.

Effect of ion and neutral sputtering on single crystal TiO2

Abstract Alteration of the structure and composition of solid surfaces under energetic ion or neutral particle impact is a major concern in surface analysis, mainly in connection with depth profiling. It has been established that preferential sputtering occurs in many compounds and systems and that this leads to chemical transformations. Titanium compounds, especially the oxides, possess various stoichiometric and non-stoichiometric states and thus offer a suitable vehicle for investigating these effects. This paper reports studies on the reduction of single crystal TiO 2 by He, Ar and N 2 ion and fast atom bombardment. Attempts have been made in this study to comprehensively characterize the chemical and electronic state of the ion or neutral bombarded single crystalline TiO 2 surfaces by X-ray Photoelectron Spectroscopy (XPS). Differences observed in the extent of bombardment induced reduction due to various incident species (He, He + , Ar, Ar + , N 2 , N 2 + have been discussed and explanations of these differences in terms of a compensating electron leakage current have been proposed.

A study of the compositional changes in chemically etched, Ar ion bombarded and reactive ion etched GaAs(100) surfaces by means of ARXPS and LEISS

Abstract The effects of chemical etching, noble gas ion bombardment and reactive ion etching on GaAs(100) surfaces was investigated by angle resolved X-ray photoelectron spectroscopy (ARXPS) and low energy ion scattering spectroscopy (LEISS). The results show that at the “as received” GaAs surface, Ga oxide is the major component, resulting in a Ga concentration slightly higher than As. Chemical cleaning by hydrochloric acid (at a HCl(conc.) to H2O ratio of 1:1) followed by solvent washing efficiently removed the oxide layer, however, ARXPS showed that strong As enrichment occurs at the cleaned GaAs surface. Ion bombardment was carried out using 3 keV Ar ions with a beam current density of 1 μA cm−2 for a period of 50 min. XPS results show that at steady state the ion bombarded GaAs surface is depleted in As ( As Ga ≈ 0.8 ), but ARXPS indicates an As increase at the very surface. This is further confirmed by Ne+ LEISS analysis, which shows in the top layer the As concentration is increased by 50% after ion bombardment. The results indicate that bombardment induced compositional changes in this surface are due to Gibssian segregation. The results of reactive ion etching in a 200 W Freon 12 plasma for a period of 5 min at 60 mTorr, showed that this apparently low damage process also produces significant compositional changes in the surface. The report illustrates the benefits of using complementary surface analytical techniques in such studies.

XPS and LEISS studies of ion bombarded GaSb, InSb and CdSe surfaces

Abstract Ion bombardment effects in GaSb, InSb and CdSe crystal surfaces were studied with a combination of X-ray photoelectron spectroscopy (XPS) and low energy ion scattering spectroscopy (LEISS). Both XPS and LEISS showed that neglecting surface contamination, the composition of the crystal surfaces prior to ion bombardment were close to their stoichiometric values of 1:1. During 3 keV Ar+ beam bombardment, XPS analysis showed that the atomic ratios of Sb Ga , Sb In and Se Cd in the bombarded surfaces decreased from 1 to 0.71, 0.92 and 0.87, respectively. LEISS results, indicated that these ratios increased to 3.33, 1.63 and 1.32, respectively. The variances between XPS and LEISS measurements are attributed to a difference in the sampling depth between the two techniques, and give a clear indication of how ion bombardment changes the surface composition of these compound semiconductors. These changes may be described in terms of bombardment-induced Gibbsian segregation.

A study of nitrogen implantation in aluminium—a comparison of experimental results and computer simulation

Abstract It is known that nitrogen ion implantation into aluminium leads to the formation of AlN. The aim of this work is to investigate the effect of ion energy, current density and dose on low energy nitrogen ion implantation. For this purpose, aluminium bulk samples, with a purity of 99.9%, were implanted with molecular nitrogen ions (N 2 + ) at energies of 2, 3, 4 and 5 keV with a current densities of 1 μA cm −2 and 5 μA cm −2 for each ion energy. The ion doses for these experiments range from 6×10 16 and 3×10 17 ions cm −2 . The concentration profiles of nitrogen ions implanted into aluminium were measured by X-ray Photoelectron Spectroscopy (XPS) and these were compared with the profiles created using computer simulation models SUSPRE [SUSPRE, Surrey University Sputter Profile Resolution from Energy deposition program V (1.4), 1987] and SATVAL [J. Sielanko, W. Szyszko, Surf. Sci. 161 (1985) 101; J. Sielanko, W. Szyszko, Nucl. Instr. Meth. Phys. Res. B 16 (1986) 101]. The chemical composition and chemical structure of the implanted aluminium were investigated by XPS and Angle Resolved X-ray Photoelectron Spectroscopy (ARXPS).

A study of thermally induced segregation of magnesium in aluminium-magnesium alloys by means of AES

The thermally induced segregation of Mg in a 1% Mg/Al alloy in the temperature range 225 to 350 degrees C has been studied by means of Auger electron depth profiling. An activation energy for the process has been determined and a linear relationship was found between the amount of Mg enrichment in the surface region and temperature. The results suggest that the segregation is chemically driven by the greater affinity of Mg for O.

Effects of low energy particle beam bombardment on solid surfaces

Abstract Low energy rare gas ion bombardment is used extensively in surface cleaning and conditioning in applications such as semiconductor processing, in surface analytical techniques such as Auger and X-ray photoelectron spectroscopies for cleaning and depth profiling and as a primary beam in other techniques such as ion scattering and secondary ion mass spectrometry. It is always appreciated that such bombardment can produce substantial chemical changes in the surface, particularly in semiconducting and insulating samples. This paper discusses bombardment induced damage in surfaces and describes series of experiments to investigate the importance of beam energy, beam flux density and charge of the bombarding particle. As a vehicle for these investigations, bombardment induced chemical reduction of oxides of niobium and titanium were studied. In these investigations X-ray photoelectron spectroscopy was employed to identify changes in chemical state of the oxides with bombardment. The results of the investigations show little variation in damage with beam energy in the range 1–5 keV, whilst beam flux density has a significant effect. It is further found that neutrals produce substantially less damage in bombarded surfaces than do ions of the same species, energy and flux. Models are proposed which explain the results in terms of surface binding energy effects, mass effects and the influence of charge induced compensating leakage currents.

Experimental and simulated XPS depth profiles of low-energy high dose nitrogen implanted into aluminium

In the paper the XPS measurements of aluminium samples implanted with low energy, high dose nitrogen ions are presented. The experimental results are compared with those obtained from a Monte-Carlo computer simulation. The influence of collisions atomic mixing and ion-bombardment-induced segregation on the distortion of the measured depth profile of implanted ions is discussed.

Effects of low-energy ion beam bombardment on metal oxides

This paper describes a study of Ar ion bombardment damage in metal oxides. In the energy range 1 to 5 keV, preferential oxygen removal and reduction of the oxides was found to depend on ion current density, but to be independent of beam energy.