A comparison of the static SIMS and G‐SIMS spectra of biodegradable homo‐polyesters

Static SIMS (SSIMS) is a surface analytical technique capable of providing molecular chemical information from solids. A major barrier to the wider take‐up of the technique is the complexity associated with the interpretation of SSIMS spectra. Quality of the interpretation depends on the expertise of analysts and making references to the limited mass spectral libraries. For many materials, there are no SSIMS library spectra. A new library‐independent method, G‐SIMS, is capable of facilitating the interpretation of SSIMS data. G‐SIMS spectra contain parent fragments, which are formed without substantial degradation or rearrangements, and highlight molecular fragments, which are directly related to the surface. In our study, G‐SIMS has been tested on medically relevant biodegradable polyester series, including poly (glycolic acid) (PGA), poly‐l‐(lactic acid) (PLA), poly‐β‐(hydroxybutyrate) (PHB) and poly‐ε‐(caprolactone) (PCL). The polyester series chosen here have closely related structures, which allow us to explore the capabilities of G‐SIMS. The G‐SIMS spectra have facilitated the identification of different polyesters by exhibiting mainly characteristic ions, representative of the polymers' molecular structures. The results also indicated that for the chosen polyester series, the larger the repeating monomer structures, the smaller the maximum number of repeat units were seen in the G‐SIMS spectra. The G‐SIMS spectra for the homologous polyester series have provided an insight into the fragmentation mechanisms as a function of repeating monomer molecular weights and structures. Copyright © 2008 John Wiley & Sons, Ltd.     

Quantitative analysis of styrene‐pentafluorostyrene random copolymers by ToF‐SIMS and XPS

Poly(styrene) (PS), poly(2,3,4,5,6‐pentafluorostyrene) (5FPS) and their random copolymers were prepared by bulk radical polymerization. The spin‐cast polymer films of these polymers were analyzed using X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). The surface and bulk compositions of these copolymers were found to be same, implying that surface segregation did not occur. The detailed analysis of ToF‐SIMS spectra indicated that the ion fragmentation mechanism is similar for both PS and 5FPS. ToF‐SIMS quantitative analysis using absolute peak intensity showed that the SIMS intensities of positive styrene fragments, particularly C₇H₇⁺, in the copolymers are higher than the intensities expected from a linear combination of PS and 5FPS, while the SIMS intensities of positive pentafluorostyrene fragments are smaller than expected. These results indicated the presence of matrix effects in ion formation process. However, the quantitative approach using relative peak intensity showed that ion intensity ratios are linearly proportional to the copolymer mole ratio when the characteristic ions of PS and 5FPS are selected. This suggests that quantitative analysis is still possible in this copolymer system. Copyright © 2005 John Wiley & Sons, Ltd.     

Extracting information on the surface monomer unit distribution of PLGA by ToF‐SIMS

The surface chemistry of a range of random poly l‐lactide‐co‐glycolide (PLGA) materials has been investigated using XPS, static secondary ion mass spectrometry (SSIMS) and gentle secondary ion mass spectrometry (G‐SIMS). The estimated mole fraction of lactide units provided by SSIMS was in good agreement with bulk composition and appeared not to have been affected by contamination. Conversely, XPS assessment of lactide compositions was unreliable due to hydrocarbon contamination contributions. In this study, we propose a novel model to demonstrate that by using SSIMS it is possible to infer the degree of trans‐esterification for PLGA co‐polymers synthesised from a mixture of lactide and glycolide homo‐dimers. This was determined by introducing two independent parameters, the ratio of trans‐esterified bonds to the total number of ester bonds, P_T, and the lactide composition. The model has indicated that, for this set of polymers, P_T was approximately 0.25. Furthermore, we have demonstrated that G‐SIMS successfully identified the structurally important key fragments leading to direct identification. Analysis by G‐SIMS showed that the glycolic acid units from all PLGA compositions are emitted in a lower energy‐fragmentation process than lactic acid units. Copyright © 2008 John Wiley & Sons, Ltd.     

Investigation of block depth distribution in PS‐b‐PMMA block copolymer using ultra‐low‐energy cesium sputtering in ToF‐SIMS

Directed self‐assembly of block copolymers (BCPs) is a promising candidate for next generation nanolithography. In order to validate a given pattern, the lateral and in‐depth distributions of the blocks should be well characterized; for the latter, time‐of‐flight (ToF) SIMS is a particularly well‐adapted technique. Here, we use an ION‐TOF ToF‐SIMS V in negative mode to provide qualitative information on the in‐depth organization of polystyrene‐b‐polymethylmethacrylate (PS‐b‐PMMA) BCP thin films. Using low‐energy Cs⁺ sputtering and Bi₃⁺ as the analysis ions, PS and PMMA homopolymer films are first analyzed in order to identify the characteristic secondary ions for each block. PS‐b‐PMMA BCPs are then characterized showing that self‐assembled nanodomains are clearly observed after annealing. We also demonstrate that the ToF‐SIMS technique is able to distinguish between the different morphologies of BCP investigated in this work (lamellae, spheres or cylinders). ToF‐SIMS characterization on BCP is in good agreement with XPS analysis performed on the same samples. Copyright © 2013 John Wiley & Sons, Ltd.     

Degradation of poly(acrylates) under SF5+ primary ion bombardment studied using time‐of‐flight secondary ion mass spectrometry. 2. Poly(n‐alkyl methacrylates)

Polyatomic primary ions offer low penetration depth and high damage removal rates in some polymers, facilitating their use in the molecular depth profiling of these polymers by secondary ion mass spectrometry (SIMS). This study is the second in a series of systematic characterizations of the effect of polymer chemistry on degradation under polyatomic primary ion bombardment. In this study, time‐of‐flight SIMS (ToF‐SIMS) was used to measure the damage of ～90 nm thick spin‐cast poly(methyl methacrylate), poly(n‐butyl methacrylate), poly(n‐octyl methacrylate) and poly(n‐dodecyl methacrylate) films under extended (～2 × 10¹⁴ ions cm^?2) 5 keV SF₅⁺ bombardment. The degradation of the poly(n‐alkyl methacrylates) were compared to determine the effect of the length of the alkyl pendant group on their degradation under SF₅⁺ bombardment. The sputter rate and stability of the characteristic secondary ion intensities of these polymers decreased linearly with alkyl pendant group length, suggesting that lengthening the n‐alkyl pendant group resulted in increased loss of the alkyl pendant groups and intra‐ or intermolecular cross‐linking under SF₅⁺ bombardment. These results are partially at variance with the literature on the thermal degradation of these polymers, which suggested that these polymers degrade primarily via depolymerization with minimal intra‐ or intermolecular cross‐linking. Copyright © 2004 John Wiley & Sons, Ltd.     

ToF‐SIMS and computation analysis: Fragmentation mechanisms of polystyrene,polystyrene‐d5, and polypentafluorostyrene

We studied the time‐of‐flight secondary ion mass spectrometry fragmentation mechanisms of polystyrenes—phenyl‐fluorinated polystyrene (5FPS), phenyl‐deuterated polystyrene (5DPS), and hydrogenated polystyrene (PS). From the positive ion spectra of 5FPS, we identified some characteristic molecular ion structures with isomeric geometries such as benzylic, benzocyclobutene, benzocyclopentene, cyclopentane, and tropylium systems. These structures were evaluated by the B3LYP‐D/jun‐cc‐pVDZ computation method. The intensities of the C₇H₂F₅⁺ (m/z = 181), CyPent‐C₉H₃F₄⁺ (m/z = 187), CyPent‐C₉H₄F₅⁺ (m/z = 207), and CyPent‐C₉H₂F₅⁺ (m/z = 205) ions were enhanced by resonance stabilization. The positive fluorinated ions from 5FPS tended to rearrange and produce fewer fluorine‐containing molecular ions through the loss of F (m/z = 19), CF (m/z = 31), and CF₂ (m/z = 50) ion fragments. Consequently, the fluorine‐containing polycyclic aromatic ions had much lower intensities than their hydrocarbon counterparts. We propose the fragmentation mechanisms for the formation of C₅H₅⁺, C₆H₅⁺, and C₇H₇⁺ ion fragments, substantiated with detailed analyses of the negative ion spectra. These ions were created through elimination of a pentafluoro‐phenyl anion (C₆F₅⁻) and H⁺, followed by a 1‐electron‐transfer process and then cyclization of the newly generated polyene with carbon‐carbon bond formation. The pendant groups with elements of different electronegativities exerted strong influences on the intensities and fragmentation processes of their corresponding ions.     

Repair of defects created by Ar+ sputtering on graphite surface by annealing as confirmed using ToF‐SIMS and XPS

Defects were created on the surface of highly oriented pyrolytic graphite (HOPG) by sputtering with an Ar⁺ ion beam, then characterized using X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) at 500°C. In the XPS C1s spectrum of the sputtered HOPG, a sp³ carbon peak appeared at 285.3 eV, representing surface defects. In addition, 2 sets of peaks, the C_x⁻ and C_xH⁻ ion series (where x = 1, 2, 3...), were identified in the ToF‐SIMS negative ion spectrum. In the positive ion spectrum, a series of C_xH₂^+• ions indicating defects was observed. Annealing of the sputtered samples under Ar was conducted at different temperatures. The XPS and ToF‐SIMS spectra of the sputtered HOPG after 800°C annealing were observed to be similar to the spectra of the fresh HOPG. The sp³ carbon peak had disappeared from the C1s spectrum, and the normalized intensities of the C_xH⁻ and C_xH₂^+• ions had decreased. These results indicate that defects created by sputtering on the surface of HOPG can be repaired by high‐temperature annealing.     

Investigation of ionic liquids under Bi‐ion and Bi‐cluster ions bombardment by ToF‐SIMS

A systematic study of five different imidazolium‐based room temperature ionic liquids, 1‐butyl‐3‐methylimidazolium acetate, 1‐butyl‐3‐methylimidazolium nitrate, 1‐butyl‐3‐methylimidazolium iodide, 1‐butyl‐3‐methylimidazolium hexafluorophosphate and 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide were carried out by means of time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) in positive and negative ion mode. The compounds were measured under Bi‐ion and Bi‐cluster ions (Bi_2–7⁺, Bi_{3, 5}²⁺) bombardment, and spectral information and general rules for the fragmentation pattern are presented. Evidence for hydrogen bonding, due to high molecular secondary cluster ions, could be found. Hydrogen bonding strength could be estimated by ToF‐SIMS via correlation of the anionic yield enhancement with solvent parameters. Copyright © 2010 John Wiley & Sons, Ltd.     

The characteristic fragment ions and visualization of cationic starches on pulp fiber using ToF‐SIMS

Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) was used to investigate the distribution of cationic starch on pulp fiber. To identify the characteristic fragment ions of the cationic starches, deuterium‐labeled cationic starches were prepared and analyzed using ToF‐SIMS. The starch 2‐hydroxypropyltrimethylammonium chloride derivative generated characteristic fragments at m/z 58 and 59, which were identified as [H₂C?N(CH₃)₂]⁺ and [N(CH₃)₃]^+·, respectively. The fragmentation patterns were also suggested. From the imaging analysis, the adsorption of the cationic starch on fibers was uneven on individual fibers, as well as between fibers. This may have been on account of fiber morphology and structure. On examining scanning electron microscope (SEM) images, the quaternary ammonium starch derivative (QS) did not penetrate the fiber. No migration of cationic starch was observed under various drying conditions. Copyright © 2007 John Wiley & Sons, Ltd.     

Static SIMS analysis of carbonate on basic alkali‐bearing surfaces

Carbonate is a somewhat enigmatic anion in static secondary ion mass spectrometry (SIMS) because abundant ions containing intact CO₃^2? are not detected when analyzing alkaline‐earth carbonate minerals common to the geochemical environment. In contrast, carbonate can be observed as an adduct ion when it is bound with alkali cations. In this study, carbonate was detected as the adduct Na₂CO₃·Na⁺ in the spectra of sodium carbonate, bicarbonate, hydroxide, oxalate, formate and nitrite and to a lesser extent nitrate. The appearance of the adduct Na₂CO₃·Na⁺ on hydroxide, oxalate, formate and nitrite surfaces was interpreted in terms of these basic surfaces fixing CO₂ from the ambient atmosphere. The low abundance of Na₂CO₃·Na⁺ in the static SIMS spectrum of sodium nitrate, compared with a significantly higher abundance in salts having stronger conjugate bases, suggested that the basicity of the conjugate anions correlated with aggressive CO₂ fixation; however, the appearance of Na₂CO₃·Na⁺ could not be explained simply in terms of solution basicity constants. The oxide molecular ion Na₂O⁺ and adducts NaOH·Na⁺ and Na₂O·Na⁺ also constituted part of the carbonate spectral signature, and were observed in spectra from all the salts studied. In addition to the carbonate and oxide ions, a low‐abundance oxalate ion series was observed that had the general formula Na_2?xH_xC₂O₄·Na⁺, where 0 < x < 2. Oxalate adsorption from the laboratory atmosphere was demonstrated but the oxalate ion series also was likely to be formed from reductive coupling occurring during the static SIMS bombardment event. The remarkable spectral similarity observed when comparing the sodium salts indicated that their surfaces shared common chemical speciation and that the chemistry of the surfaces was very different from the bulk of the particle. Copyright © 2003 John Wiley & Sons, Ltd.     

Analysis of thin films and molecular orientation using cluster SIMS

A study of phenylalanine films of different thicknesses from submonolayer to 55 nm on Si wafers has been made using Bi_n⁺ and C₆₀⁺ cluster primary ions in static SIMS. This shows that the effect of film thickness on ion yield is very similar for all primary ions, with an enhanced molecular yield at approximately 1 monolayer attributed to substrate backscattering. The static SIMS ion yields of phenylalanine at different thicknesses are, in principle, the equivalent of a static SIMS depth profile, without the complication of ion beam damage and roughness resulting from sputtering to the relevant thickness. Analyzing thin films of phenylalanine of different thicknesses allows an interpretation of molecular bonding to, and orientation on, the silicon substrate that is confirmed by XPS. The large crater size for cluster ions has interesting effects on the secondary ion intensities of both the overlayer and the substrate for monolayer and submonolayer quantities. This study expands the capability of SIMS for identification of the chemical structure of molecules at surfaces. © Crown copyright 2010.     

Cationization of dendritic macromolecule adsorbates on metals studied by time‐of‐flight secondary ion mass spectrometry

Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) was utilized to study dendritic macromolecules with various architectures, such as dendrons, dendrimers and hyperbranched polyesters prepared from bis‐(hydroxymethyl)propionic acid (Bis‐MPA) and a series of hyperbranched polyethers based on 3‐ethyl‐3(hydroxymethyl)oxetane. The measurements were performed on spin‐coated thin films of the branched molecules (D) onto silicon, chemically etched copper foil and silver‐coated wafers. They showed weak signatures of molecular ions by proton capture (D + H)⁺ in the high mass range of the spectra (m/z > 400). On the contrary, cationization of the intact molecules with alkali or transition metal ions such as Na⁺, Cu⁺ or Ag⁺ was observed. High‐intensity quasi‐molecular ions (D + M)⁺ (with M = Na⁺, Cu⁺ or Ag⁺) allowed the studied polymers to be identified. The whole molecular species were observed for Bis‐MPA dendrons and dendrimers up to 3000 Da for hydroxyl or acetonide‐terminated derivatives. The success of the so‐called cationization experiments with metal substrates compared with analysis of molecular adsorbates on silicon is highlighted. The ToF‐SIMS sensitivity appeared useful to provide information about the molecular end‐groups or to highlight incomplete reaction occurring during some deprotection step of the synthesis. Only uncationized fragments of low masses were detected for the hyperbranched polyesters. This result suggested the effect of molecular asymmetry and/or flattening of the molecules on the substrates, which hampered the molecule lift‐off efficiency. Nevertheless, the hyperbranched polyethers were characterized based on the peak distribution of intensities, which allowed estimation of their molecular weight average. This work was intended to illustrate the capabilities of ToF‐SIMS to analyse dendritic polymers on surfaces. Copyright © 2003 John Wiley & Sons, Ltd.     

Degradation of poly(acrylates) under SF5+ primary ion bombardment studied using time‐of‐flight secondary ion mass spectrometry. 3. Poly(hydroxyethyl methacrylate) with chemical derivatization

Molecular depth profiling of polymers by secondary ion mass spectrometry (SIMS) has focused on the use of polyatomic primary ions due to their low penetration depth and high damage removal rates in some polymers. This study is the third in a series of systematic characterizations of the effect of polymer chemistry on degradation under polyatomic primary ion bombardment. In this study, time‐of‐flight SIMS (ToF‐SIMS) was used to assess 5 keV SF₅⁺‐induced damage of ～90 nm thick spin‐cast poly(2‐hydroxyethyl methacrylate) (PHEMA) and ～130 nm thick trifluoroacetic anhydride‐derivatized PHEMA (TFAA‐PHEMA) films. The degradation of these polymers under extended SF₅⁺ bombardment (～2 × 10¹⁴ ions cm^?2) was compared to determine the effect of the pendant group chemistry on their degradation. The sputter rate and ion‐induced damage accumulation rate of PHEMA were similar to a poly(n‐alkyl methacrylate) of similar pendant group length, suggesting that the addition of a terminal hydroxyl group to the alkyl pendant group does not markedly change the stability of poly(n‐alkyl methacrylates) under SF₅⁺ bombardment. The sputter rate and ion‐induced damage accumulation rate of TFAA‐PHEMA were much higher than a poly(n‐alkyl methacrylate) of similar pendant group length, suggesting that derivatization of the terminal hydroxyl group can significantly reduce degradation of the polymer under SF₅⁺ bombardment. This result is in good agreement with the literature on the thermal and radiation‐induced degradation of fluorinated poly(alkyl methacrylates), which suggests that the electron‐withdrawing fluorinated pendant group increases the probability of depolymerization. Copyright © 2004 John Wiley & Sons, Ltd.     

Ultrashallow depth profiling using SIMS and ion scattering spectroscopy

The accuracy of ultrashallow depth profiling was studied by secondary ion mass spectrometry (SIMS) and high‐resolution Rutherford backscattering spectroscopy (HRBS) to obtain reliable depth profiles of ultrathin gate dielectrics and ultrashallow dopant profiles, and to provide important information for the modeling and process control of advanced complimentary metal‐oxide semiconductor (CMOS) design. An ultrathin Si₃N₄/SiO₂ stacked layer (2.5 nm) and ultrashallow arsenic implantation distributions (3 keV, 1 × 10¹⁵ cm^?2) were used to explore the accuracy of near‐surface depth profiles measured by low‐energy O₂⁺ and Cs⁺ bombardment (0.25 and 0.5 keV) at oblique incidence. The SIMS depth profiles were compared with those by HRBS. Comparison between HRBS and SIMS nitrogen profiles in the stacked layer suggested that SIMS depth profiling with O₂⁺ at low energy (0.25 keV) and an impact angle of 78° provides accurate profiles. For the As⁺‐implanted Si, the HRBS depth profiles clearly showed redistribution in the near‐surface region. In contrast, those by the conventional SIMS measurement using Cs⁺ primary ions at oblique incidence were distorted at depths less than 5 nm. The distortion resulted from a long transient caused by the native oxide. To reduce the transient behavior and to obtain more accurate depth profiles in the near‐surface region, the use of O₂⁺ primary ions was found to be effective, and 0.25 keV O₂⁺ at normal incidence provided a more reliable result than Cs⁺ in the near‐surface region. Copyright © 2007 John Wiley & Sons, Ltd.     

Proton transfer and isotope‐induced reaction in aniline cluster ions

The proton transfer (PT) and other intraclusters reactions occurring after electron ionization of aniline clusters (PhNH₂)_N are investigated by the time‐of‐flight mass spectrometry. The mass spectra are recorded for different expansion conditions leading to the generation of different cluster sizes. Several fragment ions are shown to originate from intracluster reactions, namely, [Ph]⁺, [PhNH₃]⁺ and [Ph–N–Ph]⁺. Reaction schemes are proposed for these ions starting with the PT process. The mass region beyond the monomer mass is dominated by cluster ions (PhNH₂)_n⁺ accompanied by satellites with ±H and +2H. In experiments with deuterated species, new fragment ions are identified. The aniline isotopomer d₅‐PhNH₂ yields the fragment ions (PhNH₂)_n?(N–Ph–NH₂)⁺. Analogical series is observed in experiments with d₇‐PhND₂, and additional fragments occur corresponding to (PhND₂)_n?(D₂N–ND–Ph–ND–ND₂)⁺ ions. The possible reaction pathways to these ions and the unusual isotope effects are discussed. Copyright © 2015 John Wiley & Sons, Ltd.     

ToF‐SIMS for the characterization of hyperbranched aliphatic polyesters: probing their molecular weight on surfaces based on principal component analysis (PCA)

A series of 2,2‐bis(hydroxymethyl)propionic acid (Bis‐MPA) hyperbranched aliphatic polyesters with different molecular weights (generations) is analysed for the first time by time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). The main negative and positive low‐mass fragments are identified in the fingerprint part of the spectra (m/z < 400) and are principally assigned to fragmentation of the Bis‐MPA repeating units. In addition, it is shown that the fragmentation pattern is highly affected by the functional end‐groups. This is illustrated for a phthalic acid end‐capped hyperbranched polymer and for an acetonide‐terminated dendrimer analog. Also, typical fragments assigned to the ethoxylated pentaerythritol core molecule are detected. These ions show decreasing intensities with increasing molecular weight. This intensity dependency on the generation is used to calibrate the molecular weight of hyperbranched polyesters on the surface. To obtain quantitative information, a principal component analysis (PCA) multivariate statistical method is applied to the ToF‐SIMS data. The influence of different normalization procedures prior to PCA calculation is tested, e.g. normalization to the total intensity, to the intensities of ions assigned to the Bis‐MPA repeating unit or to intensities of fragments due to the core molecule. It is shown that only one principal component (PC1) is needed to describe most of the variance between the samples. In addition, PC1 takes into account the generation effect. However, different relationships between the PC1 scores and the hyperbranched mass average molecular weights are observed depending on the normalization procedure used. Normalization of data set ion intensities by ion intensities from the core molecule allows linearization of the SIMS intensities versus the molecular weight and allows the hyperbranched polymers to be discriminated up to the highest generations. In addition, PCA applied to ToF‐SIMS data provides an extended interpretation of the spectra leading to further identification of the correlated mass peaks, such as those of the Bis‐MPA repeating unit (terminal, dendritic and linear) and those of the core molecule. Finally, the work presented demonstrates the extreme potential of the static ToF‐SIMS and PCA techniques in the analysis of dendritic molecules on solid surfaces. Copyright © 2003 John Wiley & Sons, Ltd.     

Molecular identification of Asian lacquers from different trees using Py‐GC/MS and ToF‐SIMS

Traditional Asian lacquers are natural products with highly valued properties, including beauty, gloss, and durability. Pyrolysis‐gas chromatography/mass spectrometry is the technique of choice to study insoluble polymeric lacquer films. In the present study, pyrolysis‐gas chromatography/mass spectrometry results showed that the pyrolysis products of lacquer films were different for all of the studied trees, with urushiol derivatives detected in Toxicodendron vernicifluum from China, Japan, and Korea; laccol in Toxicodendron succedaneum from Vietnam; and thitsiol in Gluta usitata from Myanmar. Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) was also used to characterize the Asian lacquers, avoiding the time‐consuming and destructive processes of other techniques. The ToF‐SIMS spectra provided structural characterization of a series of urushiol, laccol, and thitsiol derivatives for T vernicifluum from China, Japan, and Korea; T succedaneum from Vietnam; and G usitata from Myanmar, respectively. To differentiate the ToF‐SIMS results for the different Asian lacquer films, principal component analysis was used because it can extract differences in the spectra and indicate what peaks are responsible for these differences. The results indicate that lacquer films from different lacquer trees can be very different. Therefore, ToF‐SIMS with principal component analysis is suitable for the characterization and differentiation of Asian lacquer films in cultural heritage applications.     

Chemical discrimination of multilayered paint cross sections for potential forensic applications using time‐of‐flight secondary ion mass spectrometry

Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) equipped with a bismuth imaging source and an argon gas cluster ion beam (GCIB) was used to image polished cross‐sections of four automotive multilayer paint samples. Secondary ion mass spectrometry chemical imaging of the individual layers was possible after a GCIB sputter ion dose of (7 × 10¹⁵) ions/cm² was applied for the removal of polishing residue, at which point the chemical composition of the individual clear coats could be distinguished using principal components analysis. For the differentiation of the four clear coat chemistries, only four secondary ion peaks were necessary; C₂H₅O⁺ (m/z 45.04), C₉H₉NO₂⁺ (m/z 163.09), and C₁₀H₁₁NO₂⁺ (m/z 177.10) that appeared to be fragments of the carbamate‐based clear coat, and C₇H₁₁⁺ (m/z 95.09) that was strongly associated with the polyurethane‐based clear coat. Clear identification of the four paint samples based on this short peak list highlights the strength of the SIMS technique as a potential forensic approach to discriminate automotive paints and suggests that many more variables could be included in the multivariate and statistical analysis to differentiate a wider range of clear coat chemistries.     

Time‐of‐flight SIMS characterization of hydrolysed organofunctional and non‐organofunctional silanes deposited on Al,Zn and Al–43.4Zn–1.6Si alloy‐coated steel

In this paper Al, Zn and Al–43.4Zn–1.6Si (AlZn) alloy‐coated steel have been treated with the organofunctional silane γ‐mercaptopropyltrimethoxysilane (γ‐MPS) and the non‐organofunctional silane 1,2‐bis(triethoxysilyl)ethane (BTSE). Also, a two‐step treatment of metal substrates was performed: the metal substrates were treated with the BTSE silane followed by a γ‐MPS treatment. The influence of metal substrate and the pH value of the silane film properties were investigated using time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). The results show that the BTSE silane is fully hydrolysed but the γ‐MPS silane is not. The presence of negative ions of the type HSi_xO_y^? indicates that both types of silane films are highly cross‐linked via Si–O–Si bonds. The two‐step treatment gave a γ‐MPS silane layer on top of the BTSE silane layer but the thickness of the total silane film become thinner than for a single BTSE film, indicating that some of the BTSE is dissolved during the γ‐MPS deposition step. Furthermore, the ToF‐SIMS results show that the thiol group of the γ‐MPS silane is oxidized. Finally, no major influence, either in the positive or the negative mass spectra, from the different metal substrates could be detected for the silane films investigated. Copyright © 2003 John Wiley & Sons, Ltd.