J. A. van den Berg

MIAMI: Microscope and ion accelerator for materials investigations

A transmission electron microscope (TEM) with in situ ion irradiation has been built at the University of Salford, U.K. The system consists of a Colutron G-2 ion source connected to a JEOL JEM-2000FX TEM via an in-house designed and constructed ion beam transport system. The ion source can deliver ion energies from 0.5 to 10 keV for singly charged ions and can be floated up to 100 kV to allow acceleration to higher energies. Ion species from H to Xe can be produced for the full range of energies allowing the investigation of implantation with light ions such as helium as well as the effects of displacing irradiation with heavy inert or self-ions. The ability to implant light ions at energies low enough such that they come to rest within the thickness of a TEM sample and to also irradiate with heavier species at energies sufficient to cause large numbers of atomic displacements makes this facility ideally suited to the study of materials for use in nuclear environments. TEM allows the internal microstructu...

Neutral and ion beam SIMS of non-conducting materials

Abstract Energetic neutral beams are increasingly being used as an alternative to ion beams for the analysis of low conductivity materials in secondary ion mass spectrometry, since their use greatly alleviates the problems caused by sample charging. After a brief review of the history of this development, this paper reviews various methods for producing inert gas atom beams of energies in the 0.5–15 keV range and a number of neutral gun designs based on these methods are discussed. They include the saddle-field atom gun, capillaritron, a conventional electron impact source based ion/atom gun and a novel gun producing a raster-scanned micro focused (⩾ 5 μm) beam of either atoms or ions. The effects of sample charging are discussed with special reference to a low extraction field configuration. A careful control of the surface potential, which is possible under either ion or atom bombardment in conjunction with charge compensating electron beams, can provide positive and negative spectra with a substantial molecular cluster ion contribution. Secondary ion mass spectra of insulating targets under ion (+electron) or atom bombardment are qualitatively similar in that the same characteristics molecular fragment ions occur. Differences in peak height distribution are at least partially explainable in terms of a less precise control of the surface potential in the case of ion and electron bombardment. On the other hand, essential differences between the two types of bombardment are observed in the damage rate in some polymer materials and the sputter rate in a range of low conductivity materials. These experiments, carried out after careful calibration procedures, provide evidence for the existence of a charge state induced damage mechanism and a sunstantial electronic sputtering contribution in these materials under ion bombardment.

A comparison of atom and ion induced SSIMS—Evidence for a charge induced damage effect in insulator materials

Abstract A static secondary ion mass spectrometry (SSIMS) study of two very low conductivity materials, polystyrene and niobium pentoxide, using on the one hand a primary ion beam with electron neutralisation, and on the other, atom bombardement, shows that whilst the initial spectra obtained were quite similar, subsequent damage effects were much greater under ion impact conditions. For an equivalent flux density the half-life of the polystrene surface structure was four times longer under atom bombardment. Significant reduction of the niobium surface was observed under ion bombardment whereas an equivalent atom flux had little apparent effect on the surface oxidation state. These data suggest that the requirement to dissipate the charge delivered to the sample by the primary ion beam contributes significantly to the damage mechanisms in electrically insulating materials.

Evidence of a charge induced contribution to the sputtering yield of insulating and semiconducting materials

Following the recent observation in this laboratory of a charge induced damage effect in insulators under inert gas ion bombardment, the influence of the charge state of the beam (ion or atom) on the sputtering yield of insulating and semiconducting materials has been investigated. A series of sputter measurements has been carried out on Au, Ta2O5, Si, GaAs, and glass using calibrated ion and atom fluxes. For this purpose a recently developed gun capable of producing raster‐scanned, microfocused energetic ion or atom beams was employed. While for the conductor Au, as expected, no effect was seen, for the remaining materials sputter yield increases of up to 150% were observed under ion bombardment which implies the existence of a substantial electronic sputtering effect in insulators and semiconductors due to low‐energy ion bombardment.

A scanned microfocused neutral beam for use in secondary ion mass spectrometry

The construction of a gun capable of producing a microfocused (FWHM=5 μm) beam of Ar atoms at 10 keV for use in secondary electron and SIMS imaging of insulating samples is described. The design is based on the principle of neutralizing an ion beam by charge transfer subsequent to rastering and microfocusing, and therefore utilizes a final focusing lens with long working distance (60 mm). Neutral beam intensities of up to 20% of the focused ion beam can be produced. The performance of the gun is illustrated by secondary‐electron and secondary‐ion images of insulators.

A Comparative Study of Organic Polymers by SIMS and FABMS

Recent SIMS studies of polymer film surfaces [1,2] have identified and investigated several practical problems which may limit the applicability of the SIMS technique to these materials. These problems include (a) the high rate of ion beam damage, (b) the need for charge neutralisation leading to (c) the uncertainty of surface potential and (d) the possibility of electron stimulated desorption (ESD) of secondary ions.

A combined HREELS and SSIMS study of the adsorption of co on Ru/Cu and Ru/Au bimetallic surfaces

Abstract CO adsorption on bimetallic Ru/Au and Ru/Cu surfaces, prepared by depositing Cu or Auon a Ru(0001) single crystal at 540 K or 1110 K, has been studied with HREELS and SSIMS. The data show that CO adsorbs on Ru/Au surfaces in the linear coordination as is found on clean Ru(0001). On Ru/Cu surfaces the HREELS spectra for CO adsorbed at 300 K indicate a pertubation of coordination and binding energy in agreement with earlier SSIMS and TPD studies. Studies at low adsorption temperatures (120 K) show that CO adsorbs on Ru and Cu sites as well as into a new adsorption state. The data are discussed in terms of the mutual involvement of Ru and Cu in the adsorption process.

Insitu study of processes taking place on silicon surface during its bombardment by CFx/Ar ions: Etching versus polymerization

The application of a Kaufman ion source in the study of the etching/polymerization processes taking place at the surface of a silicon substrate being exposed to ion beams generated from CF4/Ar gas mixtures is reported. The processes were analyzed by means of in situ mass and energy spectroscopy of the secondary ions sputtered from the substrate surface and the charge‐exchange ions, respectively. These analytical methods confirmed the growth of the polymer C–F thin films on the silicon surface at higher concentrations of CF4 in the mixture. It was found that there existed a primary beam threshold energy above which the polymer thin film stopped growing and the etch yield of silicon atoms was increased. The simplified activated growth model presented here describes this behavior qualitatively as a competition between creative and destructive processes leading to deposition and removal of the thin polymer film, respectively.

Examination of the surface structure of zeolites by fast atom bombardment mass spectrometry (FABMS). Loewensteins rule

Fast atom bombardment mass spectrometry (FABMS) is used, in the negative ion mode, to investigate the presence of paired aluminium species in zeolites and in aluminas. Results do not support the systematic breaking of Loewensteins rule in zeolite A.

Surface analysis using electron beam SNMS, applications and investigations of sputter yields

We have designed and constructed a system of optics for electron impact postionisation SNMS. The design is based on an existing parallel plate energy filter commercially operational at UMIST. The system operates with ‘state of the art’ efficiency in the SNMS mode of operation (a postionisation efficiency of 10−3 to 10−4), without significant degradation of the SIMS operation. Calibration of the SNMS mode of the system has been undertaken using standardised samples, cross-calibrated by Optical Emission Spectroscopy. These studies revealed reproducibility of < 10% in the relative sensitivity factors, and relative sensitivity factors have been assigned to several elemental species. From these studies a detection limit of < 0.01 at.% was obtained for most elemental species at Ar+ primary beam current of less than 10 ωA. Studies of inAsxP1-x have been used to demonstrate the linearity of SNMS for Quantitative Analysis as well as revealing the homogeneity of the analysed layers. The effects of surface roughness on the efficiency of the collection optics will also be discussed. SNMS has been applied to the investigations of the total sputter yields of some multicomponent materials. Changes in the sputter yields of copper, zinc and aluminium alloys with composition have been studied by monitoring the variations in detected sputtered neutral signal. The significance of this, particularly in the field of depth profile analysis is obvious.