Depth profiling vacuum conditions

In quadrupole-based SIMS instruments, mass separation is achieved by passing the secondary ions down a path surrounded by four rods excited with various AC and DC voltages. Different sets of AC and DC conditions are used to direct the flight path of the selected secondary ions into the detector. The primary advantage of this kind of spectrometer is the high speed at which they can switch from peak to peak and their ability to perform analysis of dielectric thin films and bulk insulators. The ability of the quadrupole to switch rapidly between mass peaks enables acquisition of depth profiles with more data points per depth, which improves depth resolution. Additionally, most quadrupole-based SIMS instruments are equipped with enhanced vacuum systems, reducing the detrimental contribution of residual atmospheric species to the mass spectrum. 

The photoelectrochemical behavior of ZnSe-coated CdSe thin Aims (both deposited by vacuum evaporation on Ti) in polysulflde solution has been described by Russak and Reichman [112] and was reported to be similar to MIS-type devices. Specifically, Auger depth profiling showed the ZnSe component of the (ZnSe)CdSe heterostructures to convert to ZnO after heat treatment in air, thus forming a (ZnO)CdSe structure, while the ZnO surface layer was further converted to a ZnS layer by cycling the electrode in polysulfide electrolyte. This electrochemically generated ZnS layer provided an enhanced open-circuit potential compared to CdSe alone. Efficiencies as high as 5.4% under simulated AM2 conditions were recorded for these electrodes. 

Chemical characteristics and the oxidation state of elements in the nearsurface layer ( 5 nm) of a sample are recorded by photoelectrons that are produced by an X-ray beam. When this technique is combined with intermittent ion sputtering, data on depth distribution can be obtained. X-ray photoelectron spectroscopy goes beyond elemental analysis to provide chemical information such as distinguishing Si-Si from Si-O bonds. Elements from Li to U may be analysed with detection levels at 0.5% under high vacuum conditions. Raster scanning techniques produce images with a spatial resolution of 26 pm and depth profiles of 1 pm thick are possible (Mossotti et al., 1987 Wilson and Bums, 1987). 

In the depth-profiling analysis of steel by GD-MS, initial degassing caused serious interference problems independent of whether fast or slow erosion rates were adopted. Thermal degassing under vacuum conditions in the ion source before igniting the discharge has been shown to be helpful. 

H- and 20% N2. In the profile there Is no evidence of diffusion of SI Into the Tl. There was enough oxygen In the furnace tube to prevent any formation of a silicide. Following annealing In a vacuum environment a silicide was formed as shown by the sputter depth profile In Figure 14. A result similar to that of the forming gas case would occur If annealing was done under poor vacuum conditions. 

In addition, adjustment factors were reported to be required for specific elements whose concentrations were being over estimated, i.e. those of H, C, and O (van der Heide et al. 1998). Subsequent studies carried out under improved vacuum conditions within a Cameca ims-6f revealed that these factors were most likely to account for the adsorption of H2,02, and various gas phase-based organics onto the respective sputtered surfaces during acquisition of the energy-dependent depth profiles (van der Heide, unpublished observation). Note As covered in Section 4.2.1.1, molecular adsorption occurs even under high and ultrahigh vacuum conditions, i.e. one monolayer can form in as short a time as 10 s at 10 Torr. It is only the rate that is affected (see Relations 4.3 and 4.4). 

Surface Chemical Composition. The atomic composition of catalyst surfaces plays a decisive role for the catalyst properties. Electron and ion spectroscopies (48) are surface-sensitive analytical tools, which provide information on the atomic composition within the topmost atomic layers. The information depth, that is, the number of atomic layers contributing to the measured signal, depends on the method used. Concentration profiles can be obtained by sputter etching of the surface by ion bombardment. The application of these particle spectroscopies requires ultrahigh vacuum (UHV) conditions. 

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