A. Benninghoven

Interaction of nitrogen and ammonia plasmas with polystyrene and polycarbonate studied by X-ray photoelectron spectroscopy, neutron activation analysis and static secondary ion mass spectrometry

The interactions of NH3 and N2 plasmas with the surfaces of polystyrene (PS) and bisphenol-A polycarbonate (PC) have been studied with X.p.s. and SSIMS. Primary amino groups could be detected at the surfaces of both polymers after treatment with the NH3 plasma but not with the N2 plasma, with the aid of derivatization reactions with salicylaldehyde and 5-bromosalicylaldehyde. PC differs in its reactivity from PS with respect to its ease of undergoing chain scission during the plasma treatments, which results in modified structures of low molecular weight at the surface. The surface coverage of primary amino groups on PS after treatment with the NH3 plasma was determined by means of neutron activation analysis after derivatization of these groups with 5-bromosalicylaldehyde and estimated to be approximately 0.5 amino groups per nm2.

Surface analysis by secondary ion mass spectrometry (SIMS)

Abstract Static secondary ion mass spectrometry (static SIMS) supplies detailed information on the atomic and molecular composition of the uppermost monolayer of a solid. This information is obtained by mass analysis of sputtered secondary ions emitted from this layer during keV primary ion bombardment. Damage to the uppermost monolayer is minimized by applying extremely low primary ion fluences. Progress in static SIMS over the past 30 years is described by following the most important developments in instrumentation, i.e. the introduction of single-ion counting techniques, quadrupole and time-of-flight mass analyzers, charge compensation devices, focused ion beams for imaging, UV laser postionization of sputtered neutrals and the on-line combination of SIMS with other devices for surface modification and analysis. Today, static SIMS allows high performance surface analysis of samples of any material, geometry and conductivity. In particular the atomic and molecular composition of real world samples, very often insulators and covered by complex mixtures of atomic and molecular surface components, can be obtained with high sensitivity and high lateral resolution. Present day applications of static SIMS include microelectronics, catalysis and polymer research as well as clinical analysis, environmental monitoring and all kinds of microstructure technologies. Fundamental research, in particular on the mechanism of molecular ion formation, is still in its very beginning.

Secondary Ion Mass Spectrometry SIMS V

A brief description of studies of the atom-surface interaction using densityfunctional methods is given. The ionization probability of atoms sputtered from metal surfaces is then discussed using results of these studies in conjunction with a resonant tunnelling approach. Good agreement of this theory with experimental data of Yu on the sputtering of adsorbed alkali atoms is obtained. We begin our discussion with a brief outline of the calculation of the groundstate properties of an atom interacting with a metal surface a fixed distance away. [1] We simplify the description of the metal substrate by using the jellium model to represent it: that is, the semi-infinite lattice of positive ions of the metal is smeared out into a semi-infinite homogeneous positive background. This model eliminates much of the detail of the substrate (which is now specified only by the value of its average electron density), but it is able to represent many of the properties of the metal that will interest us here. [1] Our study of the metal-atom system is based on the density-functional theory of inhomogeneous electron systems due to HOHENBERG, KaHN and SHAM. [2] The equations that must be solved self-consistently to obtain the electron density distribution have a Hartree-like form, with a potential that includes not only electrostatic but exchange and correlation effects as well. For the latter we make the commonly used local-density approximation: the relevant exchange and correlation properties in any volume element are taken to be those of a uniform infinite electron gas with a density equal to that in the volume element. [2] When an atom interacts with a system whose electronic states form a continuum, the discrete levels of the atom which are degenerate with the continuum broaden into resonances. The resonances formed in this way when Li, Si and CI atoms interact with a high-electron-density metal are shown in Fig. 1 (at their calculated equilibrium separations). [3] (Explicitly, what is shown is the differ-

Design and performance of a reflectron based time‐of‐flight secondary ion mass spectrometer with electrodynamic primary ion mass separation

In many secondary ion mass spectrometry (SIMS) investigations, the total number of generated secondary ions is limited by the amount of sample material available. This is the case in surface reaction studies as well as in organic and inorganic trace analysis or imaging SIMS. In such cases a time‐of‐flight mass spectrometer has some considerable advantages: quasisimultaneous detection of all masses, unlimited mass range, and very high transmission. We have developed a high‐resolution reflectron based time‐of‐flight secondary ion mass spectrometer with a new electrodynamic mass separation and beam chopping technique based on a pulsed 90° deflection of the primary ion beam. A primary ion pulse width of less than 1.5 ns has been obtained. Second‐order energy focusing in the flight path of the secondary ions is achieved by a two‐stage reflectron. A mass resolution m/Δm=13 000 and a dynamic range of five orders of magnitude have been obtained with this instrument.

Optimized time-of-flight secondary ion mass spectroscopy depth profiling with a dual beam technique

High resolution depth profiling has been performed in a time-of-flight secondary ion mass spectroscopy (TOF-SIMS) instrument equipped with independent ion sources for sputtering (crater formation) and for SIMS analysis. In this dual beam mode a low energy sputter gun (Cs or any gas ion) allows a free selection of optimum sputter conditions with regard to depth resolution and matrix optimization. For secondary ion generation an independent high energy ion beam, optimized with regard to focussing and secondary ion yield (Ga or gas ion source) is applied. For different sputter gases (Ar, Xe, O2, and SF6), energies (0.3–2 keV) and angles of incidence a systematic investigation of B layers in Si and GaAlAs multilayers has been carried out. Decay lengths of 0.53 nm were achieved for low energy sputtering of B layers in Si with 0.6 keV SF5+. In this dual beam mode the depth profiling performance of TOF-SIMS exceeds that of state of the art quadrupole and magnetic sector field instruments in several fields of app...

High mass resolution surface imaging with a time‐of‐flight secondary ion mass spectroscopy scanning microprobe

This article describes first applications of a time‐of‐flight secondary ion mass spectroscopy (TOF‐SIMS) scanning microprobe, based on a high mass resolution TOF‐SIMS instrument, combined with two pulsed primary ion sources: (a) 10 keV Ga liquid metal ion source (LMIS), probe size: 0.5–1 μm; (b) 10 keV electron impact (EI) ion source (Ar+,Xe+,O+2), probe size 4–10 μm. The detection limits for elemental and molecular surface species as a function of probe size are discussed. At a lateral resolution of 1 μm secondary ion images with about 1000 counts/pixel can be acquired in about 30 min. The high useful yields achieved by TOF‐SIMS allows the analysis of submonolayers of inorganic as well as organic materials at high lateral resolution. Currently up to 24 secondary ion images for different masses and a complete mass spectrum can be acquired simultaneously. The performance of the instrument is demonstrated by multielemental and molecular imaging of inorganic and organic patterns on Si wafers. Secondary ion i...

A time‐of‐flight mass spectrometer for static SIMS applications

A high performance time‐of‐flight secondary‐ion mass spectrometer equipped with a mass selected pulsed primary ion source, an angle and energy focusing time‐of‐flight analyzer, and a high efficiency single‐ion counting detector is described. The instrument can be applied for trace analysis of organic as well as inorganic material for the detection, identification, and structural analysis of large organic molecules in the pico‐ and femtomol range, as well as for the undisturbed SIMS investigation of surface structures very sensitive to ion bombardment. Spectra of Teflon, a fully protected tetranucleotide and a nonapeptide are reported.

Time‐of‐flight secondary ion mass spectrometry of polymer materials

Secondary ion formation from polystyrene standards with well‐defined molecular weight distributions between 103 and 106 amu has systematically been investigated. Maximum yields of cationized fragments and oligomers are obtained from silver substrates covered by about one monolayer of polymer material. Intact oligomers of polystyrene are detected in the mass range up to 10 000 amu. Disappearance cross sections of sputtered molecules are correlated to the size of the desorbed species and increase almost linearly with mass. Transformation probabilities of cationized oligomers decrease by about three orders of magnitude between 1000 and 10 000 amu. Number and weight average molecular weights (Mn , Mw ) determined from peak intensities of intact polymer molecules compare well with data from gel permeation chromatography. A correction of Mn and Mw for decreasing transformation probabilities is necessary for broad molecular weight distributions. The formation of high molecular weight fragment ions can be explain...

Time‐of‐flight secondary ion mass spectrometry of insulators with pulsed charge compensation by low‐energy electrons

A new charge compensation system for time‐of‐flight (TOF) secondary ion mass spectrometry is described. A pulsed low‐energy electron source (10 eV) in combination with a pulsed extraction voltage of the TOF analyzer allows low‐energy electrons to reach the target in the relatively long period of time between two excitation pulses. Low‐energy electrons allow self‐adjusting of the surface potential. Sample damages by these electrons are not detectable. Effects due to electron stimulated desorption are suppressed by pulsing the anode of the electron source. Compensation is possible for the accumulation of positive as well as negative spectra. With this experimental arrangement we investigated a variety of insulating materials (e.g., thick polymer films, glasses, ceramics). In all cases we found stable and reproducible spectra, even of insulators with extremely low conductivity.

Static secondary ion mass spectrometry analysis of polycarbonate surfaces. Effect of structure and of surface modification on the spectra

Abstract The positive and negative ion mass spectra of the surfaces of polycarbonate derived from bisphenol A and polycarbonate derived from the bisphenol of acetophenone, and of bisphenol A and the bisphenol of acetophenone are presented. The spectra were obtained with a time-of-flight static secondary ion mass spectrometer. Comparison of the spectra of the four mentioned compounds made it possible to deduce the structures of characteristic ions. The interaction of amines with the surface of polycarbonate derived from bisphenol A could be analysed in a very detailed manner with the aid of the negative ion spectra. Some aspects of the interaction of hydrogen and oxygen plasmas with this polymer are discussed with reference to the spectra. Chain scissions were one of the processes occurring during the plasma treatments.