Positive SIMS Research Articles

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) of polyisoprenes

Polyisoprenes (PIPs) with average molecular weights from 650 to 800,000 Da have been studied by time-of-flight secondary ion mass Spectrometry (TOF-SIMS) in the static mode. Polymer samples were bombarded by argon primary ions, and positive SIMS spectra were collected. Effects of branching and unsaturation in the polymer structure on ion formation were studied. The pendant methyl group showed little tendency to fracture as a cation. In the low mass region, CnH2n−1+ appeared to be more intense than CnH2n+1+, attributed to the double bond structure of polyisoprene. Additionally, ion formation varied as a function of polymer molecular weight. Cationized intact oligomers and fragments dominate the high mass region. Oligomer distributions were used to calculate average molecular weights for polyisoprenes. A statistical chain scission mechanism was used to qualitatively explain the formation of five clusters within a unique fragmentation pattern. Detailed studies of the cluster structure pointed out that each cluster contained several species having varied degrees of unsaturation. It is believed that double bond rearrangements occur.

Structural characterization of BaTiO 3 films by sol-gel method using mono-substituting chelating agent

BaTiO 3 films have been deposited onto Pt Si substrates by repeated spin-coating and heat-treatment of precursors prepared by a sol-gel process using Ti(O- iPr) 4, Ba(CH 3COO) 2, and chelating agent CH 3COCH 2COCH 3. These films exhibit cubic phase structure and possess desired (110) orientation. Representative fragments Ti +, TiO +, Ba + and BaOH + from BaTiO 3 lattices are observed in the positive static SIMS spectrum. A well-defined interface between a BaTiO 3 film and a Pt Si substrate suggests that the proposed method is capable of depositing BaTiO 3 films onto Pt Si substrates without Si diffusion from underlying Pt Si substrates.

Evidence for Nondestructive Adsorption of Dialkyl Sulfides on Gold

The nondestructive adsorption of long chain dialkyl sulfides on gold is reported. Self-assembled monolayers of decanethiol, didecyl disulfide, and didecyl sulfide were prepared and characterized by XPS, grazing-angle FT-IR, wettability studies, and TOF-SIMS. The first three techniques provide evidence that well-packed monolayers are formed. The positive SIMS spectrum of didecyl sulfide showed fragments that originate from intact dialkyl sulfide attached to gold without C−S bond cleavage. Our results underline the generally accepted nondestructive adsorption process of dialkyl sulfides and contradict the recently reported cleavage of one of the alkyl sulfur bonds of sulfides upon adsorption.

ToF SIMS study of the desorption of emulsifiers from polystyrene latexes

AbstractThe desorption of emulsifiers from the particle surface of polystyrene latexes prepared by emulsion polymerization has been studied by Time‐of‐Flight Secondary Ion Mass Spectrometry (ToF SIMS). Two polystyrene latexes prepared with respectively sodium dodecyl sulphate and sodium dodecylbenzene sulphonate as emulsifiers were compared. It has been shown that the quasi‐molecular, parent ions and the characteristic fragments of the emulsifiers can easily be observed in positive and negative ToF SIMS. But these ions are more sensitive in the negative mode. The results have shown that after extensive purification with mixed‐bed ion‐exchange resins, the emulsifier was totally absent on the latex prepared with sodium dodecyl sulphate and that only traces of the emulsifier exist on the latex prepared with sodium dodecylbenzene sulphonate. These results suggest that strong acid emulsifiers can be desorbed by mixed‐bed ion‐exchange resins.

Energy analysis in positive SIMS with Cs + beams

A study using a primary Cs + beam to carry out positive SIMS on conductive samples is presented. The energy distribution of positive secondary ions was measured and the sputter yield, S + was calculated for several elements. The significantly different energetic behavior found between the secondary cesium ions and those ejected from the target will be discussed. Finally, the best conditions to perform positive SIMS with such a primary beam will be described.

Wien-filtered Cs + beam for SIMS: source description

A compact cesium ion source with a Wien filter is described. This source has been developed in order to produce a pure beam of cesium ions for positive SIMS analysis. The ions are produced by a surface ionization ion emitter. The initial beam is about 99% pure and the remaining 1% is removed via the Wien filter. An asymmetric einzel lens at the end provides the focusing of the beam on the target. A short description of the source is presented as well as the measured final beam characteristics.

Static secondary ion mass spectroscopic investigations of deuterated poly (ethylene terephthalate)

AbstractThe positive and negative ion static SIMS spectra of poly(ethylene terephthalate) (PET) deuterium labeled on either the ethylene glycol units or the terephthalate units were obtained and compared to those of unlabeled PET. These data confirm the ion structure assignments previously reported and allow the assignment of the origins and structures of most of the remaining peaks. The majority of the ions derive logically from the PET structure. A major mode of fragmentation f the PET chains is shown to be the break‐up of ester linkages to produce a carboxylic acid and a vinyl ester. This involves predominate transfer of a hydrogen atom from the glycol unit to the newly formed acid group. Minor, but interesting, ions have been detected which result form the recombination of fragments. These ions have structures not directly derived from the original polymer backbone and may add to the difficulties involved in analyzing the static SIMS spectra of ‘unknown’ surfaces as they suggest atomic connectivities which are not present on the original surface.

Carbon-Black-Elastomer Interaction

Abstract A number of different techniques were applied to measure carbon-black-surface reactivity and the level of black-polymer interaction in four different elastomer systems (SBR, IIR, NR, and NBR) representing differences in unsaturation, crystallinity and polarity. Known within-grade surface activity variations were based on partial graphitization of an N121-type carbon black. The surface activity of different black grades was studied as a function of variations in both surface area and DBPA. Direct measurements of carbon-black-surface reactivity were based on hydrogen analysis, SIMS, IGC, and moisture adsorption. In-rubber measurements included bound rubber, SIMS of cut surfaces, and an interaction parameter, σ/η, which is derived from the slope (σ) of the stress-strain curve at low elongations, and (η), the ratio of dynamic modulus (E′) at 1% and 25% DSA. The following trends were observed: 1. The σ/η values provided a good measure of black-polymer interaction in all four polymer systems for either the within-grade or across-grade comparisons. 2. Higher σ/η values were indicated for SBR and NBR, followed by NR and IIR in that order. 3. SBR indicated the greatest sensitivity for bound-rubber measurements in terms of distinguishing within-grade variations in black-polymer interaction, followed by IIR, NR, and NBR in that order. 4. Positive SIMS on dry carbon black indicates the presence of complex hydrocarbon structures suitable for chemical reactivity at the carbon-black surface. 5. SIMS analyses on the dry carbon blacks exhibited intensity variations in the negative hydrocarbon fragments which were in line with the within-grade variations in hydrogen content. 6. SIMS analyses on the cut-rubber compound surfaces showed overall variations in intensity which were proportional to the range and level of the bound-rubber measurements. The most meaningful variations were recorded for SBR and IIR. 7. Heats of adsorption derived from IGC measurements with different adsorbates showed an excellent correlation with black-polymer interaction for the within-grade studies. Measurements across grades did not correlate as well with the in-rubber measurements, but the best results were obtained using styrene as the adsorbate. 8. The within-grade moisture adsorption measurements showed excellent agreement with IGC and the other techniques for the N121 series of heat-treated carbon blacks.

Relative positive-ion yields from transition-metal oxide systems under dynamic secondary ion mass spectrometry conditions

In this work, first-row transition-metal oxides and several series of mixed first-row transition-metal oxides have been examined under dynamic SIMS conditions.For studies on the mixed oxides, relative sensitivity factors have been derived for a given type of mixed oxide from positive SIMS spectra, which can be used to quantitatively analyse other mixed oxides of that type.In addition, an investigation was made to determine the factors which control relative ion intensities observed in positive SIMS spectra recorded for mixed transition-metal oxides. Attempts to correlate experimental relative ion intensities with solid-state properties such as bulk composition, lattice parameter or metal–oxygen bond strength in the solid met with limited success. However, evidence was obtained for the observed relative ion intensities being controlled by the relative stability of the ions produced in the vapour phase above the solid. Relative ion and neutral partial pressures in the plasma above the sputtered region of a solid appear to be controlled by ion–molecule equilibria.

A study of secondary ion emission from silicon under improved experimental conditions

Experimental study of secondary ion emission from a clean silicon surface bombarded with a primary argon ion beam in the keV energy range under uhv is one of the most important fundamental works for SIMS. The experimental results obtained by different authors have been collected, compared and critically reviewed. In order to get reliable experimental results the main difficulties have been studied and the experimental conditions have been controlled and improved. It has been shown that the reliable experimental results can only be obtained under carefully controlled experimental conditions. The better experimental results of positive and negative SIMS spectra from a clean silicon surface under uhv, its dependence upon the primary argon ion energy, the influence of the primary ion energy on the yield of singly and multiply charged atomic ions and cluster ions, some interesting phenomena of negative SIMS spectrum of silicon and a brief discussion are presented in this paper.

SIMS/AES characterization of the initial oxidation of an iron—chromium—molybdenum alloy and its base metals at room temperature

AbstractLow‐temperature oxidation of a FeCrMo alloy and their base metals was investigated by static and dynamic positive and negative SIMS combined with AES Ar+ sputter profiling at 5 keV primary beam energy. In situ oxidation was carried out for 0.3–10000 Langmuir (L) oxygen exposure after sputter cleanning. Static SIMS revealed oxidation of chromium at the outer surface at very low exposures (<0.5 L). With increasing exposures, mainly Fe2O3 was formed at the surface. Dynamic SIMS and AES concentration profiles revealed a multilayer structure with an outer Fe2O3 layer followed by a layer rich in chromium oxide. Oxidized molybdenum was found throughout the film and at the oxide/metal interface.

Organic reactions at interfaces: charge minimization in desorption ionization of Zwitterionic compounds

Zwitterionic compounds of the general formula R(CH 3) 2N + (CH 2) n X −1 (R = CH 3, n-C 12H 25, n-C 16H 33 or n-C 22H 45; X = CO 2, SO 3, OSO 3 or P(CH 3)O 2) and the cytidine-5′-di-phosphocholine monosodium salt, upon examination by secondary ion mass spectrometry, undergo beam-induced alkyl transfer reactions. These processes are indicated by (M + CH 3) + and (M + R) + ions in the positive ion SIMS spectra of the solid samples, while the absence of (M − CH 3) − and (M − R) − ions in the negative ion spectra suggests that the reaction does not occur by simple intermolecular alkyl transfer. The extent of alkyl transfer decreases when the sample is examined in solid NH 4Cl or p-toluenesulfonic acid ( p-TSA) or liquid triethanolamine (TEOA) matrices, supporting an intermolecular mechanism. When the negative ion spectra are recorded for the compounds in TEOA solution, each displays (M − CH 3) − or (M − R) − ions, which is interpreted as evidence for intermolecular alkyl transfer from the analyte to the nucleophilic solvent. Charge site remote fragmentation, methyl-for-sodium and hydrogen-for-sodium substitution reactions and multiple alkyl transfers are also observed. The relative abundances of the ions in the spectra of the neat samples and those diluted in solid NH 4Cl are time dependent. The extent of fragmentation increases with irradiation time until approximately a monolayer of the surface has been modified, after which fragmentation is constant. These observations are consistent with a transalkylation mechanism in which an alkyl group is abstracted from a protonated molecule by an adjacent zwitterion. This mechanism, which is thermochemically favored, suggests that minimization of the number of charges desorbed into the gas phase is a significant driving force in interfacial chemistry.

Potassium ion beams SIMS of metal samples in high vacuum

A study using a primary Cs+ beam to carry out positive SIMS on conductive samples is presented. The energy distribution of positive secondary ions was measured and the sputter yield, S+ was calculated for several elements. The significantly different energetic behavior found between the secondary cesium ions and those ejected from the target will be discussed. Finally, the best conditions to perform positive SIMS with such a primary beam will be described.

A TPD, SIMS and Δφ study of the influence of coadsorbed potassium on the adsorption and decomposition of ethylene on Pt(111)

The influence of potassium on the adsorption and decomposition of ethylene on Pt(111) has been studied using TPD, positive and negative SIMS and Δφ measurements. Potassium alters the bonding mode of ethylene and, at low coverage, increases the sticking coefficient at 100 K. Potassium inhibits ethane formation, eliminates hydrogen evolution at room temperature and induces a new hydrogen desorption peak at 420 K. Around room temperature, a new species, which we propose is ethylidene (CH 3CH=), is formed in the presence of K. This species becomes dominant for θ K between 0.07 and 0.14 ML and converts into ethylidyne at higher temperature (near 360 K). The species left on the surface after ethylidyne decomposition is characterized as CCH and it is destabilized by potassium. At larger θ K, ethylene rapidly dehydrogenates to CCH without the accumulation of ethylidyne. Decomposition of CCH leaves surface carbon, which starts to polymerize at 460 K. Throughout all these processes, CC bond cleavage is not favored.

Interfacial reactions and counterion effects in the secondary ion mass spectra of perrhenate salts

Perrhenate salts (CReO 4, CNH 4 or alkali metal), supported on graphite, have been examined by low-flux positive and negative ion SIMS. The relative abundance of ReO 4 − with respect to ReO 3 − in the spectra of the neat salts varies dramatically with the nature of the cation. LiReO 4 and NH 4ReO 4 show large ReO 3 − abundances and NaReO 4, KReO 4, and RbReO 4 show very little ReO 3 −. The fact that the ReO 3 −/ReO 4 − ratio exhibits a time dependence demonstrates that the observed reduction is an interfacial reaction; it occurs over an area of 50 Å 2/collision. The positive ion spectra also show large counterion effects, abundant clusters of the C 2ReO 4 + type only being observed for NaReO 4, KReO 4, and RbReO 4. The similarities between the spectra of 1:1 mixtures CReO 4/C′Cl and C′ReO 4/CCl (where C and C′ are alkali metal cations) suggests that intimate mixing occurs on the molecular scale when simple physical mixtures of the solid salts are subjected to ion beam bombardment. In these mixtures, cations compete to impose their characteristic effects (given above) on the spectra in the order Li + ⪢ Cs + ⪢ Rb + ⪖ K + ⪢ NH 4 + ⪢ Na +. It is therefore possible to control the nature of the mass spectrum by addition of appropriate matrix materials. In a triethanolamine (liquid) matrix, counterion effects are absent although reduction to yield, inter alia, ReO 3 − and ReO 4H 4 − is observed. These results constitute further examples of a growing number of interfacial reactions which have been encountered in the desorption methods of ionization. They also provide insights into the SIMS ionization mechanism, although they represent cases in which correlations between spectra and analyte structure are not simple.

Sims study of absorbates: I. Benzaldehyde and benzoic acid on aluminium

The adsorptions of benzoic acid and of benzaldehyde on aluminium substrates are studied by XPS and SIMS. The negative and positive SIMS spectra and the XPS spectra of benzoic acid on plasma oxidised aluminium correlate with the adsorbate structure. Benzaldehyde adsorbed on plasma oxidised aluminium gives similar XPS and SIMS spectra to those of benzoic acid in agreement with the known oxidative properties of the surface. Decreasing the amount of oxygen on the substrate before adsorption of the aldehyde results in broad C1s spectra, which are difficult to interpret. The corresponding SIMS spectra show that only a fraction of the adsorbate is now in the form of the acid. SIMS fragments are observed at much higher masses than the acid ion. These are assigned to polymeric species formed by abstraction of oxygen or water from the adsorbed molecules to give hydrocarbon residues. The relative amount of acid and polymer depends on the amount of substrate oxygen.

A comparison of positive and negative ion static SIMS spectra of polymer surfaces

AbstractNegative ion static SIMS spectra are presented for several polymers whose positive ion spectra have been well characterized previously. The negative cluster ions present in the spectra of poly‐methyl methacrylate, poly‐hydroxy ethylmethacrylate and poly‐ethylene terephthalate provide detailed information on polymer side chain and back‐bone structure complementing and clarifying the information previously only obtainable from positive ion emission. The detection and optimization of structurally informative negative cluster ions is discussed in relation to experimental parameters and the role of surface potential.

Investigation of the Anodically Formed Passive Film on Iron by Secondary Ion Mass Spectroscopy

This paper reports SIMS analysis of passive layers. Pure Fe disks are used in borate buffers of . Preelectrolysis is carried out to remove trace impurities. Potential step control of the electrode is utilized. Two types of experiments are carried out. In one, passive layers are prepared and then exposed to chloride ions for various times. In the other, films are heated at various temperatures for preselected times. The passive layers subjected to these treatments are exposed to SIMS analysis. The distribution of OH− with depth, from SIMS analysis, shows an exponential‐like decrease away from the electrode/solution interface for passive films exposed to 0.5M buffered chloride solutions for various times or heated at a given temperature for a predetermined period of time. The OH− peak heights at a fixed depth in passive layers decrease in a similar manner with increasing exposure time to chloride ions or with increasing annealing temperature for a given time period. Cl− peak heights for films exposed to chloride ion‐containing borate solutions increase rapidly for times up until breakdown, decrease sharply after breakdown, and then level off at times much longer than breakdown. O− peak heights decrease exponentially with depth for samples exposed to chloride ions and decrease linearly for specimens annealed at various temperatures for a number of different times. Corresponding Fe+ peak height data display a linear decrease with depth for chloride‐treated films and an almost constant value for layers subjected to thermal treatments. Positive SIMS O+ peak heights increase sharply for thermally treated films over a surface region of approximately 7Å, remain constant in the bulk regions, and decrease rapidly in the film/metal interfacial regions. Homogeneous films are indicated with a thickness of about 25Å. Detailed mechanistic discussions of the two principal models of passivity show that the results are in greater agreement with the amorphous hydrated polymeric oxide model than with the crystalline oxide model, in which water is considered only in terms of adsorbed water on the surface of the passive film.

Automated peak interpretation in low resolution SIMS spectra; a comparison of two algorithms

Low mass resolution secondary ion mass spectra from solid samples frequently exhibit multiple line interferences at integer mass numbers due to extensive clustering and molecule formation between constituent sample atoms. Two computer algorithms are described which try to address the problem of spectrum interpretation, i.e. the assignment of isotopic and molecular ion species (and their total specific ion currents) to the peaks observed in the mass spectrum. The algorithms are applied to a positive SIMS spectrum, a negative SIMS spectrum and a mass spectrum emitted from a liquid metal ion source; interpreted results are compared.

The quantitative application of sims to cadmium mercury telluride

Confirmation of a post sputtering ionisation mechanism proposed to explain anomalous features in the positive SIMS spectrum of CMT is given by studies of energy distributions and dependence on primary beam intensity. Despite preferential loss of mercury, meaningful depth profiles of trace elements are obtained. Evidence is given of trace element accumulation at interfaces.