Functionality of novel black silicon based nanostructured surfaces studied by TOF SIMS

A functionality of the novel black silicon based nanostructured surfaces (BS 2) with different metal surface modifications was tested by time-of-flight secondary ion mass spectrometry (TOF SIMS). Mainly two surface functions were studied: analytical signal enhancement and analyte pre-ionization effect in SIMS due to nanostructure type and the assistance of the noble metal surface coating (Ag or Au) for secondary ion formation. As a testing analyte a Rhodamine 6G was applied. Bi⁺ has been used as SIMS primary ions. It was found out that SIMS signal enhancement of the analyte significantly depends on Ag layer thickness and measured ion mode (negative, positive). The best SIMS signal enhancement was obtained at BS2 surface coated with 400 nm of Ag layer. SIMS fragmentation schemes were developed for a model analyte deposited onto a silver and gold surface. Significant differences in pre-ionization effects can play an important role in the SIMS analysis due to identification and spectra interpretation.     

SSIMS analysis of organics, polymer blends and interfaces

This paper gives a critical review on the applications of ToF SIMS in the areas of polymer additive characterization and in the study of polymer blends and interfaces. Polymer additives can readily be identified by ToF SIMS using their parent molecular ions or characteristic fragments. This analytical capability has been successfully applied to monitor the migration or segregation of additives during polymer processing. ToF SIMS is an ideal analytical tool for the study of polymer blends and interfaces because it is able to provide information on both surface composition and morphology. In combination with other analytical techniques such as AFM and XPS, ToF SIMS chemical imaging capability has opened up new horizons in the investigation of complex polymer blend systems. Finally the main advantages and limitations of ToF SIMS in these application areas are also discussed.     

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.     

The application of SIMS to the study of CO adsorption on polycrystalline metal surfaces

Secondary ion mass spectroscopy (SIMS) was used to study the adsorption of carbon monoxide on polycrystalline nickel, copper, iron, palladium and tungsten foils. The results demonstrate the ability of SIMS to distinguish, qualitatively, between molecular and dissociative adsorption. A correlation between SIMS results and those obtained by infra-red spectroscopy for molecular adsorption is also suggested.     

Three comments on single impurity-molecule spectroscopy

Three issues of interest in the present stage of development of single impurity-molecule spectroscopy (SIMS) are discussed: (i) prospects of SIMS in quantum informatics, (ii) the possibility of SIMS realization by measuring the surface enhanced Raman scattering in solids, and (iii) concentration effects in SIMS and in persistent spectral hole burning.     

Dynamic SIMS analysis of cryo-prepared biological and geological specimens

The modification of a dynamic magnetic sector secondary ion mass spectrometry (SIMS) instrument to permit the analysis of frozen biological and geological samples is described. The SIMS instrument used for this study combines SIMS analysis with the generation of ion-induced secondary electron images, allowing direct superposition of the SIMS image onto the image of cellular structures. Secondary ion maps have been acquired with sub-micron resolution, permitting the characterisation of sub-cellular elemental distributions in plant cells and human fibroblast cells, as well as the distribution of chemical impurities at grain boundaries in polar ice samples. This cryo-preparation technique clearly extends the applicability of SIMS analysis to a wide range of samples.     

Compositional analysis in the nano-regime:A SIMS perspective

A serious problem in secondary ion mass spectrometry (SIMS) analysis is its "matrix effect" that hinders the quantification of a certain species in a sample and consequently, appropriate corrective measures are taken to calibrate the secondary ion currents into respective concentrations for accurate compositional analysis. Use of "calibration standards" is necessary for this purpose. Detection of molecular MCsn+ ions (M-element to be analyzed, n=1, 2, 3,....) under Cs+ ion bombardment is a possible mean to minimize such matrix effect, enabling one to quantify without the need of calibration standards. Our recent studies on MCsn+ molecular ions aim towards the understanding of their formation mechanisms, which are important to know their effects on SIMS quantification.In-depth quantitative analysis is a major strength of SIMS for which 'depth resolution' is of significant relevance. The optimal choice of the impact parameters during SIMS analyses can play an effective role in obtaining data with ultra-high depth resolution. SIMS is possible at depth resolution in the nm or even sub-nm range, with quantifiable data obtained from the top monolayer onwards into the material. With optimized experimental conditions, like extremely low beam current (down to ～10 nA), and low bombarding energy (below 1 keV), ultra-high depth resolution SIMS has enabled interfacial composition analysis of ultra-thin films, quantum wells, heterostructures, etc. and complex low-dimensional structures with high precision and repeatability.     

Depth profiling using C60 SIMS—Deposition and topography development during bombardment of silicon

A C₆₀⁺ primary ion source has been coupled to an ion microscope secondary ion mass spectrometry (SIMS) instrument to examine sputtering of silicon with an emphasis on possible application of C₆₀⁺ depth profiling for high depth resolution SIMS analysis of silicon semiconductor materials. Unexpectedly, C₆₀⁺ SIMS depth profiling of silicon was found to be complicated by the deposition of an amorphous carbon layer which buries the silicon substrate. Sputtering of the silicon was observed only at the highest accessible beam energies (14.5 keV impact) or by using oxygen backfilling. C₆₀⁺ SIMS depth profiling of As delta-doped test samples at 14.5 keV demonstrated a substantial (factor of 5) degradation in depth resolution compared to Cs⁺ SIMS depth profiling. This degradation is thought to result from the formation of an unusual platelet-like grain structure on the SIMS crater bottoms. Other unusual topographical features were also observed on silicon substrates after high primary ion dose C₆₀⁺ bombardment.     

二次离子质谱在HL－1托卡马克研究中的应用

应用ＬＡＳ－２０００二次离子质谱表面分析系统作了如下测量：（１）测出ＨＬ－１装置的总出气量以及其主要出气组分的出气量百分比和出气峰值温度等参数；（２）对等离子体－表面相互作用进行了ＳＩＭＳ／蒙特卡洛互补分析，测出等离子体边界层中氢气量径向特征长度和氢粒子注入硅片的特征深度，估算出氢通量平均动力温度；（３）对硅收集探针的ＳＩＭＳ／ＡＥＳ分析表明，ＨＬ－１等离子体删削层中主要杂质组分为Ｏ、Ｃ、Ｎｉ、Ｍｏ和Ｃｒ，同时给出原子密度相对百分比；在ＨＬ－１装置中用原位蒸钛来吸氧、碳杂质，从而提高了等离子体纯度和品质；（４）定期检测表明，装置的器壁表面污染呈减弱趋势，这说明ＨＬ－１真空系统的设计研制及运行维护技术措施等是合适的。     

Matrix-enhanced secondary ion mass spectrometry: The Alchemist's solution?

Because of the requirements of large molecule characterization and high-lateral resolution SIMS imaging, the possibility of improving molecular ion yields by the use of specific sample preparation procedures has recently generated a renewed interest in the static SIMS community. In comparison with polyatomic projectiles, however, signal enhancement by a matrix might appear to some as the alchemist's versus the scientist's solution to the current problems of organic SIMS. In this contribution, I would like to discuss critically the pros and cons of matrix-enhanced SIMS procedures, in the new framework that includes polyatomic ion bombardment. This discussion is based on a short review of the experimental and theoretical developments achieved in the last decade with respect to the three following approaches: (i) blending the analyte with a low-molecular weight organic matrix (MALDI-type preparation procedure); (ii) mixing alkali/noble metal salts with the analyte; (iii) evaporating a noble metal layer on the analyte sample surface (organic molecules, polymers).     

High resolution quantitative SIMS analysis of shallow boron implants in silicon using a bevel and image approach

Secondary ion mass spectrometry (SIMS) is frequently used as the preferred tool for dopant profiling due to its sensitivity and depth resolution. However, as dopant profiles become shallower most, if not all of the implant profile lies in the pre-equilibrium or transient region of an SIMS depth profile. In this region sputter yield and ionisation rate vary making accurate quantification of the implant profile very difficult. These problems can be reduced through the use of much lower beam energies or oxygen flooding of the sample. However, most SIMS instruments do not have these capabilities. In this paper an alternative technique for producing an accurate depth profile of a shallow implant, using existing SIMS technology is presented.Through the fabrication of bevels with very small slope angles on a shallow boron implanted silicon via a chemical etch, SIMS ion imaging is performed on the exposed surface. Ion image data is then summed, and in conjunction with accurate measurement of the bevel morphology, a shallow boron implant profile produced. The ‘bevel-image’ profile compares very well with a profile obtained using a 1 keV oxygen beam. To ensure a good dynamic range on the ‘bevel-image’ profile it is important to clean the bevel with a HF etch, prior to imaging.     

Photoexcitation of electron-hole pairs during SIMS

During analysis with SIMS (secondary ion mass spectroscopy) a HeNe laser beam was focussed on the sample surface. While sputtering Si with oxygen ions, the laser irradiation produced a strong increase of the target current and the SIMS intensities as well. This was found for lightly p-doped Si only, whereas no effect was observed for highly p-doped or n-doped Si. To explain this we assume that a depletion layer exists under the surface oxide layer and free charged carriers are created therein by laser excitation. The laser induced effects observed in the SIMS intensity or the target current can be used for measuring the profile of an ion beam or for measuring the alignment of an ion beam at a laser marked target. In addition, laser irradiation combined with SIMS allows one to measure qualitatively both the profile of the doping impurity and its electrically active part.     

Secondary ion mass spectrometry for quantitative surface and in-depth analysis of materials

Secondary ion mass spectrometry (SIMS) is a technique based on the sputtering of material surfaces under primary ion bombardment. A fraction of the sputtered ions which largely originate from the top one or two atomic layers of the solid is extracted and passed into a mass spectrometer where they are separated according to their mass-to-charge ratios and subsequently detected. Because the sputter-yields of the individual species, coupled with their ionization probabilities, can be quite high and the mass spectrometers can be built with high efficiencies, the SIMS technique can provide an extremely high degree of surface sensitivity. Using a particular mode like static SIMS where a primary ion current is as low as 10^?11 amp, the erosion rate of the surface can be kept as low as 1 Å per hour and one can obtain the chemical information of the uppermost atomic layer of the target. The other mode like dynamic SIMS where the primary ion current is much higher can be employed for depth profiling of any chemical species within the target matrix, providing a very sensitive tool (～ 1 ppm down to ppb) for quantitative characterization of surfaces, thin films, superlattices, etc. The presence of molecular ions amongst the sputtered species makes this method particularly valuable in the study of molecular surfaces and molecular adsorbates. The range of peak-intensities in a typical SIMS spectrum spans about seven to eight orders of magnitude, showing its enormously high dynamic range; an advantage in addition to high sensitivity and high depth-resolution. Furthermore, the high sensitivity of SIMS to a very small amount of material implies that this technique is adaptable to microscopy, offering its imaging possibilities. By using this possibility in static SIMS or dynamic SIMS mode of analysis, one can obtain a two-dimensional (2D) surface mapping or a three-dimensional (3D) reconstruction of the elemental distribution, respectively within the target matrix. Secondary ion yields for elements can differ from matrix to matrix. These sensitivity variations pose serious limitations in quantifying SIMS data. Various methods like calibration curve approach, implantation standard method, use of relative sensitivity factor, etc. are presently employed for making quantitative SIMS analysis. The formation of secondary ions by ion bombardment of solids is relatively a complex process and theoretical research in this direction continues in understanding this process in general. The present paper briefly reviews the perspective of this subject in the field of materials analysis.     

Study of the structural perfection and distribution/redistribution of silicon in epitaxial GaAs films grown by molecular beam epitaxy on (100), (111)A, and (111)B substrates

Silicon distribution before and after thermal annealing in thin doped GaAs layers grown by molecular beam epitaxy on (100)-, (111)A-, (111)B-oriented substrates is studied by X-ray diffraction and SIMS. The surface morphology of the epitaxial films inside and outside an ion etch crater that arises during SIMS measurements is studied by atomic force microscopy. Distinctions in the surface relief inside the crater for different orientations have been revealed. Observed differences in the doping profiles are explained by features of the surface relief developing in the course of ion etching in SIMS measurements and by enhanced Si diffusion via growth defects.     

Quantitative secondary ion mass spectrometry of fluorocarbon polymers

Secondary ion mass spectrometry (SIMS) is used to measure quantitatively the thickness of thin (6–160 Å) polyperfluoroether films on silicon and gold surfaces. Linear relationship between ellipsometrically measured thicknesses and integrated SIMS signals is demonstrated. Time dependence of SIMS signals indicates that the polymeric films have a uniform thickness down to the thinnest layers studied. In the lower limit, the fluorocarbon polymers have extended, flat conformation due to polymer-substrate interactions. Sputtering yield and effective sputtering depth of oxygen ions are determined for these liquid polymers. It is also shown that organic adsorbates reside between the solid surface and the low surface tension fluorocarbon films.     

Molecular SIMS – A journey from single crystal to biological surface studies

The development of Static or Molecular secondary ion mass spectrometry (SIMS) is reviewed with particular reference to the journey made by the Manchester group and its collaborators. The earliest studies focussed on the application of static SIMS to single crystal surface studies. These studies successfully demonstrated that static SIMS delivered information on the delicate adsorbate state that mirrored that obtained by other surface science techniques. Subsequent application of the technique to studying the state and reactivity of bimetallic surfaces stimulated by collaboration with the Ertl group, demonstrated that static SIMS could be applied to the investigation of quite complex surface chemistry. This success stimulated the application of the technique to surface chemistry studies of much more complex systems such as polymers, ice mimics of polar stratospheric clouds, aerosols, culminating in biological systems. The need to enhance ion yields of the larger biological molecules led to the development and introduction of polyatomic primary ion beams, most notably based on C₆₀ buckminsterfullerene. This type of ion beam has transformed molecular analysis by SIMS. Not only have the yields of larger molecular ions been greatly increased, the bombardment induced damage that necessitated the static limit has been dramatically reduced such that for many materials the static limit requirement can be abandoned. A completely new analytical regime has opened up so that molecular depth profiling and 3D chemical imaging is possible. To fully realise the new capabilities for biological analysis a new generation of ToF-SIMS instrument is being developed that overcomes the compromises of pulsed beam instruments and that enables high mass resolution, high spatial resolution and high duty cycle to be attained simultaneously.     

SIMS study of the processes in buffer solutions of bioorganic systems

Enzymatic glucose oxidation in a system modeling a glucose biosensor have been investigated by SIMS with the use of a liquid matrix. The effect of some solution parameters on the reaction product (gluconic acid) yield has been analyzed. It is shown by an example of gluconolactone hydrolysis that SIMS makes it possible to study not only final but also intermediate stage of the glucose oxidation reaction.     

Introduction of ice protective film for 3D microscale analysis of biological sample

It is urgently necessary for secondary ion mass spectrometry (SIMS) analysis to overcome influence on the compositional distribution of the sample in vacuum chamber. In this study, we investigated the handling of the ice protective film in techniques such as the gallium focused ion beam (Ga FIB) etching. Here we demonstrate the technique with frozen Hymenochirus boettgeri red blood cell. The red blood cells covered with an ice protective film were cross-sectioned by using Ga FIB, and the two-dimensional SIMS mapping over the cross-section was carried out. The distributions of Na and K were observed on the cross-section and surface of red blood cell with ice protective film. This result agrees qualitatively with physiological intracellular and extracellular concentrations of vital cells. The technique used for SIMS was proved to be a reliable method, preserving the cells in their living state.     

Improved determination of phosphorus contamination during ion implantation by SRP and simulations

Experimental determination of phosphorous cross-contamination during antimony implantation is presented. As a suitable structure for this experiment, a buried layer was employed which is created by implanting antimony followed by a long diffusion process. The implanted samples were analysed by SIMS and spreading resistance (SRP) methods. SRP method has been improved by applying a correction for the carrier spilling effect. A conversion chart for p-n junction depth dependence on phosphorus doping has been calculated by program SUPREM-IV. Comparison of SRP and SIMS methods has shown that SRP method can be used for monitoring the phosphorus cross-contamination and can be easily implemented as an in-line monitor and present an alternative to expensive and time consuming SIMS analysis.     

Atoms, clusters and photons: Energetic probes for mass spectrometry

The physical mechanisms underlying the surface based mass spectrometry techniques of atomic SIMS, MALDI and cluster SIMS are discussed along with the relation of the physics to the measured quantities. In particular, there are at least two types of motion resulting from cluster bombardment in SIMS. One scenario involves the individual atoms in the cluster initiating collision cascades similar to atomic bombardment. The second mechanism involves a mesoscale motion of the cluster as a whole. This mesoscale motion can induce an organized flow of the ejected material in a plume.