Secondary Ion Mass Spectrometry Study Research Articles

Static secondary ion mass spectrometry study of the decomposition of triethylgallium on GaAs (100)

The decomposition of triethylgallium (TEGa-d0) and perdeuterated triethylgallium (TEGa-d15) on Ga-rich GaAs (100) was studied using temperature programmed static secondary ion mass spectrometry (SSIMS) and temperature programmed desorption (TPD). Isothermal and temperature programmed SSIMS spectra of the TEGa-dosed surface feature three dominant hydrocarbon ions, CH3+, C2H3+, and C2H5+, whose behavior indicates the presence of two distinct ethyl ligands. The TEGa-d15 results were equivalent to the TEGa-d0 results, with the ion masses shifted by the D and H mass differences. Both CH3+ and C2H3+ SSIMS signals exhibit the same temperature dependence, staying rather constant between 140–530 K and then decreasing rapidly between 530 and 650 K. The CH3+ and C2H3+ signals disappear over the same temperature range in which C2H4 forms and desorbs from the surface in TPD; these SSIMS signals are attributed to the surface ethyl ligands that are responsible for C2H4 formation. Ethyl ligands reacting to ethylene are l...

Growth of tin-doped indium antimonide for magnetoresistors

Magnetoresistors made from n-type indium antimonide are of interest for magnetic position sensing applications. In this study, tin-doped indium antimonide was grown by the metalorganic chemical vapor deposition technique using trimethylindium, trisdimethylaminoantimony, and tetraethyltin in a hydrogen ambient. Using a growth temperature of 370°C and a pressure of 200 Torr, it was found that the electron density in tin-doped films varied from 3.3×1016 cm−3 to 4.0×1017 cm−3 as the 5/3 ratio was varied from 4.8 to 6.8. From secondary ion mass spectroscopy (SIMS) studies, it was found that this variation is not caused by a change in site occupancy of the tin atoms from antimony to indium lattice sites, but rather to a change in the total tin concentration incorporated into the films. This dependence of tin incorporation on stoichiometry could be used to rapidly vary the doping level during growth. Undoped films grown under similar conditions had electron densities of about 2×1016 cm−3 and electron mobilities near 50,000 cm2V−1s−1 at room temperature for films that were only 1.5 µm thick on a gallium arsenide substrate. Attempts to grow indium antimonide at 280°C resulted in p-type material caused by carbon incorporation. The carbon concentration as measured with SIMS increased rapidly with increasing growth rate, to above 1019 cm−3 at 0.25 µm/h. This is apparently caused by incomplete pyrolysis of a reactant at this low growth temperature. Growth at 420°C resulted in rough surface morphologies. Finally, it was demonstrated that films with excellent electron mobility and an optimized doping profile for magnetoresistors can be grown.

Secondary ion mass spectrometry study of silicon surface preparation and the polystyrene/silicon interface

Secondary ion mass spectrometry (SIMS) is now routinely employed to obtain depth profiles in polymer films on silicon substrates, where diffusion, segregation, and ordering of deuterated polymer blend components are typically examined with a depth resolution of less than 100 Å. In some cases, diffusion or segregation behavior near the silicon surface is influenced by the extent of surface oxidation. There is also the potential for remnant moisture at the polymer/silicon interface to influence the redistribution of blend components. The effect of standard wet chemical wafer cleaning procedures on the polystyrene/silicon interface is investigated here. Deuterated solutions are employed to allow detection of remnant moisture from the cleaning/etching steps, and to indicate the extent of hydrogen termination at the polystyrene/silicon interface. Implant standards and deuterated polystyrene blends are employed to quantify the detected interfacial contaminants. The SIMS data indicate that the surface is effectively terminated by approximately one monolayer of hydrogen after an HF etch step, and by a thin oxide layer after an HCl/peroxide etch, in accord with numerous studies. There is no evidence of remnant moisture. Interfacial deuterium and oxygen are stable under 190 °C anneals. The absence of CD− secondary ions at the interface indicates that the interfacial deuterium does not become associated with adjacent polystyrene chains. Low levels of fluorine are also monitored, and the integrated fluorine concentration at the polystyrene/silicon interface is less than 0.01 monolayers of coverage.

Indium antimonide doped with manganese grown by molecular beam epitaxy

Abstract Indium antimonide is of interest for infrared detecting and emitting devices and for magnetic field sensors. In this study, indium antimonide doped with manganese and grown by molecular beam epitaxy was investigated. Secondary ion mass spectroscopy (SIMS) was used to show that the incorporation of managenese is near unity over a wide range of manganese concentrations. Manganese is observed to be an acceptor with a dopant efficiency which follows a power law in which the hole density is proportional to the manganese concentration raised to the power α. The power α depends on the growth temperature; at 300°C, α = 0.86 and at 360°C, α = 0.78. Lightly manganese doped samples have transport dominated by electrons at low temperatures due to hole freeze out, followed by holes at intermediate temperatures and finally by intrinsic electrons at high temperatures. Additional SIMS studies showed that manganese diffuses relatively slowly in indium antimonide.

Secondary Ion Mass Spectrometry of Polymers: a ToF SIMS Study of Monodispersed PMMA Standards

This paper is concerned with the effects that polymer molecular weight, casting solvent, sonification (with a non-polymer solvent) and annealing have upon the secondary ion mass spectrometry (SIMS) of polymers. Films of a series of monodispersed poly(methyl methacrylate) (PMMA) standards, Mw 2965–1200000, were prepared by solution casting from four solvents (tetrahydrofuran (THF), 2-butanone, toulene and chloroform) onto clean aluminium (Al) substrates. The PMMA films were characterized by high- and unit-mass resolution time-of-flight secondary ion mass spectrometry (ToF-SIMS). To determine the significance of variations seen in ion intensities, one PMMA sample was re-analysed 24 times, and the scatter in the absolute counts and normalized and ratioed ion intensities for specific (termed ‘key’) positive and negative ions were calculated. This provided 95% confidence error bars, which were subsequently employed. The 95% confidence limits were significantly reduced by normalizing or ratioing. Molecular weight was found to have the greatest effect in the SIMS spectra obtained, with the differences being most marked between Mw=2965 and Mw=89100. This was seen in both the total negative ion counts (m/z 31–200) and the key negative ion ratios. An explanation based on the surface concentration of chain ends is presented. Negative ion ratios were shown to be very sensitive to trace amounts of residual solvents. By annealing above the PMMA glass transition temperature Tg solvent-free films were produced from three solvents and these were spectrally indistinguishable. Solvent-free films could not be produced from THF. Residual solvent was identified by high mass resolution ToF-SIMS. Sonification with hexane, a polymer non-solvent, had a considerable effect on the total negative ion counts (m/z 31–200). No concomitant chemical changes were detected, so this effect is thought to arise from a physical perturbation of the surface. © 1997 by John Wiley & Sons, Ltd.

Influence of support material on formation of electrocatalytic thin films—a secondary ion mass spectrometry study

The influence of various support materials, such as nickel and titanium, on the structure of TiO 2, RuO 2, RuO 2/TiO 2 and IrO 2/TiO 2 electrocatalytic thin films was investigated in detail by secondary ion mass spectrometry (SIMS). The coatings were prepared by heat treatment following literature procedure. It is shown that various support materials can favor the formation and can influence the ion yield of ionic species with different oxidation states. The penetration characteristics of TiO 2 in two-component systems on the same support are influenced by the nature of the noble metal. Furthermore, changes in the structure of the coatings due to method and time of storage may be detected by SIMS analysis.

Static secondary ion mass spectrometry (SSIMS) of biological compounds in tissue and tissue-like matrices

This paper presents results of a static secondary ion mass spectrometry (SSIMS) study of molecular, pseudo-molecular and structurally significant fragment ion peaks produced from an extensive list of biomolecules analyzed as neat residues and as components in biological matrices. This study defines realistic detection limits for analysis of representative pharmaceutical compounds incorporated into tissue or tissue-like matrices using state-of-the-art time-of-flight secondary ion mass spectrometry (TOF-SIMS) techniques. Detection limits on the order of 100–1000 parts-per-million (ppm) are observed under typical analytical conditions in which the analysis areas are approximately 200 micrometer (μm) in diameter and analysis depths are 1 to 2 monolayers. Representative secondary ion images of selected biomolecules are also presented and relationships between image resolution, mass resolution and detection sensitivity are discussed.

Study of metal-polymer adhesion—A new technology: Cu plasma PIB

Adhesion between copper and n-type parylene (PA-N) has been studied. The PA-N film was deposited on Si(100) substrate by vapor deposition polymerization (VDP), and the Cu film was deposited on PA-N by plasma partially ionized beam (Plasma PIB) as well as other deposition techniques as a comparison. The adhesion strength was measured by 90° peel test after the sample was cleaved into a strip to define geometry. A peel strength of greater than 70 g/mm between the Cu film and PA-N was achieved by Cu Plasma PIB. X-ray photoelectron spectroscopy (XPS) studies found no Cu-O-C bond formation at Cu-parylene surface, while secondary ion mass spectrometry (SIMS) studies showed that a significant amount of Cu was shallowly implanted into the PA-N, with an average concentration of 1017–1018 atoms/cm3 near the interface. The results showed that a physically intermixing layer of about 100A between the two phases formed by shallow implantation of Cu into PA-N was the main mechanism of adhesion. A suggested model is proposed correspondingly.

Dynamic and static secondary ion mass spectrometry studies of the solvation of HCl by ice

H. A. Donsig and J. C. Vickerman, J. Chem. Soc., Faraday Trans., 1997, 93, 2755 DOI: 10.1039/A701724C

Transient phenomena and impurity relocation in SIMS depth profiling using oxygen bombardment: pursuing the physics to interpret the data

High detection sensitivity in bulk analysis or depth profiling by secondary ion mass spectrometry (SIMS) can only be achieved, for positively charged ions, if the nearsurface regions of the sputter eroded sample are fully oxidized. Using oxygen primary ions, a stationary oxidation state is established after some time of bombardment during which period the sputtering yield decreases and the ionization probability increases. The physical and chemical processes occurring during the transient period are reviewed with emphasis on the results for impurity analysis in silicon, i.e. the matrix material that has been studied most thoroughly in the past. The transient decrease in sputtering yield gives rise to a depth scale offset and an associated apparent shift of impurity profiles towards the surface. The effect is largest at normal beam incidence, ca. 1 nm /keV (O + 2 ), in which case silicon is fully oxidized. The transition depth, i.e. the depth sputtered before achieving a stable ion yield is about twice as large and increases as the impact angle is turned away from normal. The shift and the depth scale offset can be measured safely using thin (delta) layers of isotopically pure tracers, for example 30 Si in 28 Si. Boron delta layers can serve as secondary standards because this impurity behaves almost the same as the host silicon atoms. The profile shift observed with other common dopants may contain contributions due to unidirectional relocation, often driven by segregation away from the surface. At O + 2 energies below about 0.7 keV the transition depths fall below the thickness of typical native oxides, so that the transient changes in sputtering yield and ionization probability can disappear. The transient phenomena may be described by a simple sputtering-oxidation model that connects the depth scale offset to other observable parameters like the initial and final sputtering yield, the transition fluence and the oxide thickness.

Imaging fibrinogen adsorbed on noble metal surfaces with scanning tunneling microscopy: correlation of images with electron spectroscopy for chemical analysis, secondary ion mass spectrometry, and radiolabeling studies

Fibrinogen adsorption on gold and platinum surfaces has been studied with electron spectroscopy for chemical analysis (ESCA), secondary ion mass spectrometry (SIMS), 125I labeling, and scanning tunneling microscopy (STM). Stable images of single molecules have been obtained, but are rare. ESCA, SIMS, and labeling studies confirm that absorbed fibrinogen is present on samples at monolayer and submonolayer coverages even when STM images show only a bare substrate. Imaging is more reproducible at high coverages at which single molecules cannot be resolved. Possible explanations for the failure of STM to observe adsorbed fibrinogen molecules are discussed.

Oxygen contamination of low temperature ultrahigh vacuum-deposited Ge films on GaAs

The Fourier transform infrared absorption spectrum for the range of 500–4000 cm−1 wave numbers was measured for several Ge films deposited on GaAs using ultrahigh vacuum e-beam deposition at various substrate temperatures ranging from room temperature (RT) to 500 °C. Spectra indicate oxygen incorporation at low deposition temperatures whether or not the native oxide was removed from the substrate prior to film deposition. Using transmission electron microscopy, we show that Ge films deposited at RT and 100 °C on a (100) GaAs surface that did not have the oxides removed are amorphous while those deposited at 100 °C with the oxide removed are crystalline, but are highly defective. Secondary ion mass spectroscopy (SIMS) measurements show that the amorphous films at RT contain more than two orders of magnitude more oxygen than the films deposited at 100 °C or a single crystal film deposited at 400 °C. Oxygen-18 diffusion studies definitively show that the excess oxygen in the amorphous films percolates in from the atmosphere. SIMS studies further reveal that thermally removing the GaAs substrate surface oxide or depositing an Au film on top of the Ge film has little effect on the incorporation of oxygen.

Chemical vapour deposition and characterization of gallium oxide thin films

Gallium oxide thin films were deposited on alumina and TiO 2 substrates by metal organic chemical vapour deposition using gallium trishexafluoroacetylacetonate (Ga(hfac) 3) as precursor in the presence of oxygen. The depositions were carried out at 470°C and 2.6 kPa leading to a growth rate of 0.7 μm h −1. As-grown films appeared black, smooth and well adherent to the substrates. X-Ray photoelectron spectroscopy (XPS) analysis revealed stoichiometric Ga 2O 3 with a low carbon content (less than 5%) and almost undetectable fluorine. As-deposited Ga 2O 3 films were X-ray amorphous, but the onset of a crystallization process was evident after annealing in dry air at 700 °C. Moreover, after thermal treatment, the films became carbon free and transparent in the visible range. The effect of annealing at different temperatures on the film structure was investigated by X-ray diffraction. A phase modification from amorphous to polycrystalline Ga 2O 3 was observed after thermal treatment at temperatures from 600 to 1000 °C. As shown by secondary ion mass spectrometry (SIMS) studies, Al diffusion into Ga 2O 3 films was detected after annealing at 1000 °C when pure Al 2O 3 was used as substrate; this diffusion was completely inhibited using a TiO 2 film as buffer layer with a thickness of at least 4 μm.

Surface Morphology of a PVC/PMMA Blend Studied by ToF-SIMS

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) studies, utilizing both laterial imaging and shallow depth profiling, of a 50 :50 poly(vinyl chloride)/poly(methyl methacrylate) (PVC :PMMA) blend have confirmed the presence of a thin overlayer of PMMA on the phase-separated bulk morphology.

Secondary ion mass spectroscopy study of Au trapping and migration in the Au-irradiated YBa2Cu3O7−δ film

The range data and migration of Au in YBa2Cu3O7−δ film were studied with implanted 197Au (1.5 MeV 5×1015 Au+/cm2) as a tracer. The film was a c-axis oriented film, ∼750 nm thick, deposited by high-pressure planar dc sputtering on 〈100〉 LaAlO3. Analysis by secondary ion mass spectroscopy shows that the as-implanted Au concentration distribution is essentially Gaussian-like and the depth (R̂p) of maximum Au concentration (∼1.2 wt %) is 201 nm. The projected range (R̄p) and (R̂p) are found to be in very good agreement with the simulated data by TRIM−95, whereas the measured ‘‘straggle’’ (ΔRp*) is about 20% larger than that by TRIM−95 simulation. It has also been found that the implanted 197Au starts to migrate within the film at a temperature between 650 and 700 °C, which is much higher than that for the implanted 2H (∼175 °C) and the implanted 18O (between 250 and 300 °C) in c-oriented YBa2Cu3O7−δ films.

On the origin of blue luminescence arising from atmospheric impregnation of oxidized porous silicon

When heavily oxidized porous silicon is stored in ambient air for prolonged periods, a broad blue photoluminescence band with nanosecond decay times gradually appears. Not only PL intensity, but peak position, half-width and temperature dependence evolve with material aging. Very similar photoluminescence is shown to be characteristic of many high surface area materials stored in air for months. We stress here that hydrocarbon contamination can occur during air exposure, in addition to hydration by water vapour. Preliminary Fourier transform infrared spectroscopy and secondary ion mass spectrometry studies, together with published data on blue-emitting porous alumina and organics, suggest that the gradual build-up of low concentrations of carbonyl-related chromophores could give rise to the emergence of blue-green luminescence in aged oxidized porous Si structures.

A SIMS study on secondary ion formation during low-energy methyl ion beam deposition

A secondary ion mass spectrometry (SIMS) study has been carried out during ion beam deposition of 10–100 eV CH 3 + or CD 3 + ions on a Si(111) substrate using a highly sophisticated low-energy ion beam deposition (IBD) apparatus combined with surface analysis systems. Secondary hydrocarbon ions containing up to five carbon atoms were observed to be produced. Results obtained with CD 3 + ions showed that both ion deposition and secondary ion formation processes are different above and below an incident ion energy of 30 eV.

Secondary ion mass spectrometry studies on the formation of the valve metal oxide in ruthenium- and iridium-based mixed oxide electrodes

The process of TiO 2 evolution from titanium diisopropoxide bis-2,4-pentanedionate precursor on nickel and titanium supports was followed by secondary ion mass spectrometry. Concentration depth profiles of rutile (TiO 2) at higher temperatures showed completely different patterns for the two supports, indicating the influence of the base metal on the formation and properties of the oxide coating. The formation and surface accumulation of elemental carbon during combustion of the organic matter were followed as a function of temperature. The results obtained are in agreement with those of previous measurements by simultaneous thermogravimetry-differential thermal analysis, thermogravimetry combined with mass spectrometry and emission FTIR spectrometry.

A secondary ion mass spectrometry study of p+ porous silicon

Porous silicon layers formed on p+ substrates were investigated by secondary ion mass spectrometry technique. It has been found for the first time that the dopant impurity (boron) does not escape from the porous silicon (PS) layer during the anodization. Analysis of the boron excess in PS in relation to the crystalline substrate provides a means by which to study the porosity depth distribution. The resistivity of the PS layer has been observed to depend strongly on depth: in particular, in the high-porosity layers (50-65%) a relatively thin insulating sublayer (about 300 nm) is found to form at the surface. After annealing of the PS layers in an oxidizing atmosphere, the high-resistivity regions disappear.

A quantitative time-of-flight secondary ion mass spectrometry study of ion formation mechanisms using acid-base alternating Langmuir-Blodgett films

The effect of pre-existing acid-base proton transfer on ion formation in secondary ion mass spectrometry (SIMS) is studied with model systems constructed by Langmuir-Blodgett techniques. Reflection-Absorption FTIR was used to verify proton transfer in tri-layer LB assemblies of docosanoic acid (A) and 1-docosylamine (B). A recently developed quantitative method for quasi-molecular ions in Static SIMS was extended to Time-of-Flight SIMS. The formation of protonated base ions ((B + H) +) is highly dependent on film structure and pre-existing chemistry. The formation of the conjugate (A−H) −) carboxylate anion is more dependent on concentration of species rather than local chemistry. The implications for molecular quantitative analysis in SIMS are discussed.