Argon Gas Cluster-Ion Beam sources have become widely-used on X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) instruments in recent years, but there is little reference data on sputter yields in the literature as yet. Total sputter yield reference data is needed in order to calibrate the depth scale, of XPS or SIMS depth profiles. We previously published a semi-empirical ‘Threshold’ equation for estimating cluster total sputter yield from the energy-per-atom of the cluster and the effective monatomic sputter threshold of the material. This has been shown to agree extremely well with sputter yield measurements on a range or organic and inorganic materials for clusters of around a thousand atoms. Here we use the molecular dynamics (MD) approach to explore a wider range of energy and cluster size than is easy to do experimentally to high precision. We performed MD simulations using the ‘Large-scale Atomic/Molecular Massively Parallel Simulator’ (LAMMPS) parallel MD code on high-performance computer (HPC) systems. We performed 1150 simulations of individual collisions with a silicon (100) surface as an archetypal inorganic substrate, for cluster sizes between 30 and 3000 argon atoms and energies in the range 5 to 40 eV per atom. This corresponds to the most important regime for experimental cluster depth-profiling in SIMS and XPS. Our MD results show a dependence on cluster size as well as energy-per-atom. Using the exponent previously suggested by Paruch et al., we modified the Threshold model equation published previously to take this into account. The modified Threshold equation fits all our MD results extremely well, building on its success in fitting experimental sputter yield measurements. This work is submitted to the volume dedicated to Dr. Martin P Seah, MBE, who was a great influence on the early career of one of the authors (PJC) and who himself made many valuable contributions to the literature on sputtering as it relates to surface and interface analysis. 相似文献
In secondary ion mass spectrometry (SIMS) of organic substances, the dissociation of the sample molecules is crucial. We have developed SIMS equipment capable of bombardment, where the primary ions are argon cluster ions with kinetic energy per atom controllable down to 1 eV. We previously reported the detection of intact ions of insulin and cytochrome C using this equipment. In this paper, we present a detailed characterization of the emission of secondary ions from insulin, focusing on the difference in secondary ion yield between intact ions and fragment ions by varying the incident angle of the cluster ions. The emission intensity of the intact ions was changed drastically due to the exposed dosage and incident angle of the cluster ions in contrast to the fragment ions. We discuss these results based on the manner in which the argon-cluster ions collide with the organic solid. 相似文献
Sputter depth profiling of organic films while maintaining the molecular integrity of the sample has long been deemed impossible
because of the accumulation of ion bombardment-induced chemical damage. Only recently, it was found that this problem can
be greatly reduced if cluster ion beams are used for sputter erosion. For organic samples, carbon cluster ions appear to be
particularly well suited for such a task. Analysis of available data reveals that a projectile appears to be more effective
as the number of carbon atoms in the cluster is increased, leaving fullerene ions as the most promising candidates to date.
Using a commercially available, highly focused C60q+ cluster ion beam, we demonstrate the versatility of the technique for depth profiling various organic films deposited on
a silicon substrate and elucidate the dependence of the results on properties such as projectile ion impact energy and angle,
and sample temperature. Moreover, examples are shown where the technique is applied to organic multilayer structures in order
to investigate the depth resolution across film-film interfaces. These model experiments allow collection of valuable information
on how cluster impact molecular depth profiling works and how to understand and optimize the depth resolution achieved using
this technique. 相似文献
X‐ray photoelectron spectroscopy is used to study a wide variety of material systems as a function of depth (“depth profiling”). Historically, Ar+ has been the primary ion of choice, but even at low kinetic energies, Ar+ ion beams can damage materials by creating, for example, nonstoichiometric oxides. Here, we show that the depth profiles of inorganic oxides can be greatly improved using Ar giant gas cluster beams. For NbOx thin films, we demonstrate that using Arx+ (x = 1000‐2500) gas cluster beams with kinetic energies per projectile atom from 5 to 20 eV, there is significantly less preferential oxygen sputtering than 500 eV Ar+ sputtering leading to improvements in the measured steady state O/Nb ratio. However, there is significant sputter‐induced sample roughness. Depending on the experimental conditions, the surface roughness is up to 20× that of the initial NbOx surface. In general, higher kinetic energies per rojectile atom (E/n) lead to higher sputter yields (Y/n) and less sputter‐induced roughness and consequently better quality depth profiles. We demonstrate that the best‐quality depth profiles are obtained by increasing the sample temperature; the chemical damage and the crater rms roughness is reduced. The best experimental conditions for depth profiling were found to be using a 20 keV Ar2500+ primary ion beam at a sample temperature of 44°C. At this temperature, there is no, or very little, reduction of the niobium oxide layer and the crater rms roughness is close to that of the original surface. 相似文献
Summary Experience in obtaining accurate sodium, calcium and aluminium profiles in silicon dioxide using SIMS and Auger depth profiling is reported. With the knowledge of implantation energy and ion dose, it is possible to calculate and to realize well defined implantation profiles in special substrates with high accuracy. The technological demand is to measure this so called accurate profiles in implanted structures without alteration by the measurement. SIMS and Auger profiling have been tested in special applications to study the influence of ion sputtering on the depth distribution in membranes and to obtain accurate profiles. Experimental results are presented for the application of Auger profiling at sample edges and SIMS profiling using negative ions. In the case of Auger profiling a transformation routine was developed for using linescan and sputter profile results in combination. 相似文献
The structures developed in organic electronics, such as organic light emitting diodes (OLEDs) or organic photovoltaics (OPVs) devices always involve hybrid interfaces, joining metal or oxide layers with organic layers. No satisfactory method to probe these hybrid interfaces physical chemistry currently exists. One promising way to analyze such interfaces is to use in situ ion beam etching, but this requires ion beams able to depth profile both inorganic and organic layers. Mono- or diatomic ion beams commonly used to depth profile inorganic materials usually perform badly on organics, while cluster ion beams perform excellently on organics but yield poor results when organics and inorganics are mixed. Conversely, low energy Cs+ beams (<500 eV) allow organic and inorganic materials depth profiling with comparable erosion rates. This paper shows a successful depth profiling of a model hybrid system made of metallic (Au, Cr) and organic (tyrosine) layers, sputtered with 500 eV Cs+ ions. Tyrosine layers capped with metallic overlayers are depth profiled easily, with high intensities for the characteristic molecular ions and other specific fragments. Metallic Au or Cr atoms are recoiled into the organic layer where they cause some damage near the hybrid interface as well as changes in the erosion rate. However, these recoil implanted metallic atoms do not appear to severely degrade the depth profile overall quality. This first successful hybrid depth profiling report opens new possibilities for the study of OLEDs, organic solar cells, or other hybrid devices.
Argon cluster ions have enabled molecular depth profiling to unprecedented depths, with minimal loss of chemical information or changes in sputter rate. However, depth profiling of ultrathick films (>100 μm) using a commercial ion source oriented at 45° to the surface causes the crater bottom to shrink in size because of a combination of the crater wall angle, sputter rate differences along the trailing-edge crater wall, and undercutting on the leading-edge. The shrinking of the crater bottom has 2 immediate effects on dual-beam depth profiling: first is that the centering of the analysis beam inside the sputter crater will no longer ensure the best quality depth profile because the location of the flat crater bottom progressively shifts toward the leading-edge and second, the shifting of the crater bottom enforces a maximum thickness of the film that could be depth profiled. Experiments demonstrate that a time-of-flight secondary ion mass spectrometry instrument equipped with a 20 keV argon cluster source is limited to depth profiling a 180 μm-thick film when a 500 μm sputter raster is used and a 100 μm square crater bottom is to be left for analysis. In addition, depth profiling of a multilayer film revealed that the depth resolution degrades on trailing-edge side of the crater bottom presumably because of the redeposition of the sputtered flux from the crater wall onto the crater bottom. 相似文献