Depth profiling reference materials

Secondary ion mass spectrometry (SIMS) is by far the most sensitive surface teclmique, but also the most difficult one to quantify. SIMS is very popular in materials research for making concentration depth profiles and chemical maps of the surface. For a more extensive treatment of SIMS the reader is referred to [3] and [14. 15 and 16]. The principle of SIMS is conceptually simple When a surface is exposed to a beam of ions... 

Because of the complex nature of the discharge conditions, GD-OES is a comparative analytical method and standard reference materials must be used to establish a unique relationship between the measured line intensities and the elemental concentration. In quantitative bulk analysis, which has been developed to very high standards, calibration is performed with a set of calibration samples of composition similar to the unknown samples. Normally, a major element is used as reference and the internal standard method is applied. This approach is not generally applicable in depth-profile analysis, because the different layers encountered in a depth profile of ten comprise widely different types of material which means that a common reference element is not available. 

A quite different application of GDMS is the measurement of hydrogen and deuterium concentration, including depth profile analysis, e.g. in a gold electroplated layer on a CuSn substrate as described in reference.116 The relative sensitivity coefficient of hydrogen was evaluated by measurements of titanium standard reference material. 

Inorganic mass spectrometry requires the development of suitable reference materials, such as matrix matched standard reference materials for trace, surface (including depth profiling and microlocal) analysis and/or the creation of matrix independent calibration procedures. The development of species specific standards will be intensified for speciation studies in the future. 

Most screws of SSEs are single flighted, with Ls = Ds, referred to as square-pitched screws. The radial distance between the root of the screw and the barrel surface is the channel depth, H. The main design variable of screws is the channel depth profile that is H(z), where z is the helical, down-channel direction, namely, the direction of net flow of the material. The angle formed between the flight and the plane normal to the axis is called the helix angle, 0, which, as is evident from Fig. 6.8, is related to lead and diameter... 

Figure 7.12 Depth-profile of positronium fractions, extracted from the 3-to-2 photon ratio, for O-plasma treated samples. The scale emphasizes the relatively small Ps fractions. Legend black boxes - reference material red circles -10 min O-plasma and blue downward triangles - 2 hours O-plasma. Statistical errors are similar to the scatter of the data points.

A combined LEISS-AES-EC study was earlier undertaken at crystalline PtsCo and PtsNi alloy surfaces. It was reported that, when PtsCo and PtsNi were annealed at 1000 K, only Pt atoms existed on the outermost layer the latter was referred to as a Pt skin. This particular observation is not in agreement with the result here that Co actually co-exists with Pt at the outermost layer. Interestingly, when the PtsCo surface in the earlier study was lightly sputtered, approximately 25% of the sputtered material was Co this result suggests that Co is in fact present at the topmost layer. Why a discrepancy exists between the LEISS and depth-profile studies is unclear. But, for the difference between the present and previous LEISS work, the possibility exists that the interfacial be-... 

Neutron depth profiling has been applied in many areas of electronic materials research, as discussed here and in the references. The simplicity of the method and the interpretation of data are described. Major points to be made for NDP as an analytical technique include i) it is nondestructive il) isotopic concentrations are determined quantitatively iii) profiling measurements can be performed in essentially all solid materials, however depth resolution and depth of analysis are material dependent iv) NDP is capable of profiling across interfacial boundaries and v) there are few interferences. 

The majority of a series of shadowgraphs recorded at a laser fluence of 50 mj cm 2 are displayed in Fig. 38 and most of those from a series of experiments with a 250 mj cm 2 fluence laser are shown in Fig. 39. The time zero chosen for these photographs was at the peak of the excimer laser irradiation [209]. In this time zero reference, a photo was also taken at time=-4.8 ns for the 50 mj cm-2 fluence laser and at time=-7.2 ns for the 250 mj cm 2 fluence laser. Although both of these negative time photos were well after the beginning of the laser irradiation, neither showed any indication of shock wave formation or material expansion [94]. A depth profiler was used to measure a final ablation depth of 50 nm in one of the 50 mj cm 2 fluence case experiments and 650 nm in one of the 250 mj cm-2 fluence case experiments. 

SIMS is used for quantitative depth profile determinations of trace elements in solids. These traces can be impurities or deliberately added elements, such as dopants in semiconductors. Accurate depth prohles require uniform bombardment of the analyzed area and the sputter rate in the material must be determined. The sputter rate is usually determined by physical measurement of the crater depth for multilayered materials, each layer may have a unique sputter rate that must be determined. Depth prohle standards are required. Government standards agencies like NIST have such standard reference materials available for a limited number of applications. For example, SRM depth profile standards of phosphorus in silicon, boron in silicon, and arsenic in silicon are available from NIST for calibration of SIMS instmments. P, As, and B are common dopants in the semiconductor industry and their accurate determination is critical to semiconductor manufacture and quality control. 

The primary result of an AES depth profile analysis is an Auger transition intensity versus sputter time presentation. Quantification leading to atomic concentrations is possible when RSFs or reference materials are available. A measurement of sputter rates which depend on the sputtered material enables... 

ISO 14606 Sputter depth profiling - optimization using layered systems as reference materials ... 

Toujou, E, Yoshikawa, S., Homma, Y., Takano, A., Takenaka, H.,Tomita, M., Li, Z., Hasegawa,T., Sasakawa, K., Schuhmacher, M., Merkulov, A., Kim, H.K., Moon, D.W, Hong, T, Won, X (2004) Evaluation of BN-delta-doped multilayer reference materials for shallow depth profiling in SIMS round-robin test. Applied Surface Science, 231-232,649-652. 

Lee, J.L.S., Ninomiya, S., Matsuo, J., Gihnore, I.S., Seah, M.P., Shard, A.G. (2010) Organic depth profiling of a nanostructured delta layer reference material using large argon cluster ions. Anal. Chem., 82, 98-105. 

Oxidation of PS is commonly used to prepare tissue culture plates " or to control the distribution or behaviour of mammalian cells ( Surface-Modified Materials). Eqs (31) and (32) refer to the boxcar model, in which the profile considered for the concentration of the element or chemical function of interest vs. depth is a rectangle. More sophisticated models have been considered to simnlate ARXPS data obtained on surface-modified polymers triangular depth profile, trapezoid depth profile, profile involving several linear segments, or a continuous function. " " " In all cases, the significance of models and of fitting parameters must be examined, considering not only the sensitivity of the computed results to their variations " but also the possible errors on the experimental data and on the fixed parameters introduced. 

As in depth profiling, the signals recorded are typically those displaying the highest intensities and lowest isobaric interferences. Two examples of three-dimensional imaging are shown in Figures 5.6 and 5.7. Note Quantification of such images can be extremely difficult because of the inabUity to account for site-specific matrix effects (see Section 3.3.1.2) and/or the limitation in effective reference materials/procedures. 

The PCOR-SIMS approach attempts to correct for both the secondary ion intensity and sputter rate variations noted over the associated transient and/or interfacial region by, first, deriving the actual sputter rates and RSFs at each point of the respective depth profile for each specific matrix as analyzed under a specific set of conditions and then, secondly, applying the derived sputter rates and RSFs on a point-by-point basis to the substrate being examined such that the appropriate corrections are applied. The first step is often aided using specifically fabricated reference materials that have been fully characterized, often by various other cross-referencing techniques. 

Once a peptide map is characterized using online MS, the chromatographic profile alone can serve as a routine analytical tool to monitor the protein s primary structure and covalent modifications, and is often used for batch release or stability testing of biopharmaceuticals. However, whenever in-depth characterization of a protein is needed, such as that required for comparability studies or reference material characterization, the peptide map should be coupled with MS to ensure a thorough examination of all peptides in the map. 

---