Background

The surface chemistry of photographic film materials can be complex and therefore subject to a wide range of manufacturing problems. Identification of the cause, often on small surface defects or using inadequate surface chemical characteristics, generally requires sensitive molecular specific analytical tools with high spatial resolution. Modern surface analysis techniques such as XPS (X-ray Photoelectron Spectroscopy), ToFSIMS (Time-of-Flight Secondary Ion Mass Spectrometry) and DSIMS (Dynamic Secondary Ion Mass Spectrometry) are particularly suited to provide such types of information. The case study below shows how CSMA has been involved in helping manufacturers to troubleshoot existing processes and augment research and development efforts.

Case Study - Discolouration of Steel Sheets used to Produce Photo Film Canisters

The Problem

The purpose of this analysis was to identify the cause for the presence of brown spots and a more yellow appearance of the steel surface in the case of the defective product. Both non-printed and printed sheets were supplied. The steel surface was supposed to be electro-coated with approximately 10 nm of chromium. Initial SEM-EDX analyses conducted by the customer indicated a chromium deficiency on the problem samples and the brown spots to be iron oxide suggesting that the chromium overlayer was insufficiently thick to prevent corrosion. However, surface analysis was commissioned to further characterise the steel surfaces, with the particular questions of whether the iron oxide was the only species found in the stains, what was the nature of the yellow colouration and identify a possible cause for a lower level of chromium on the problematic sheets.

Analytical Techniques

Both XPS and ToF-SIMS were used for these analyses.

Results

Table 1. Surface chemical compositions (figures are in atomic %) from XPS.

Sample	Fe	Cr	O	C	F
Reference sample	-	8.3	41.5	46.1	4.0
Problem sample (yellow area)	4.5	3.6	38.1	50.0	3.8
Problem sample (brown stain)	10.1	trace	44.1	45.8	-

Table 2. Chromium and iron (2p) oxidation states (figure are in % of total chromium concentration).

Sample	Cr (metal)	Cr (oxides)	Fe (metal)	FeO	Fe2O3	Fe3O4
Reference sample	25%	75%	-	-	-	-
Problem sample	0%	100%	0%	40%	37%	23%

Analysis of Data

The X-Ray Photoelectron Spectroscopy data clearly showed that iron was not detected in the case of the reference sample indicating a chromium (and carbonaceous) overlayer of thickness greater than 5 nm. By contrast, iron oxides were detected in both yellow coloured and stain areas indicating that in the former case, the colouration was due to oxidation of the whole surface of the steel sheet.

In addition, the high resolution chromium spectra showed that primarily oxidised chromium was observed on the problem sample whereas a metallic state was also present for the reference sample indicating a well organised protective chromium layer on that sample.

Summary

Time of Flight Secondary Ion Mass Spectroscopy results were in agreement with the X-Ray Photoelectron Spectroscopy data where high levels of iron (and low levels of chromium) were observed on the problem sample (see spectra). In addition, for the problem sample only, the surface showed the presence of a bisphenol-A containing species. This species was suspected to be related to, or indeed the cause of, poor chromium deposition.

Figure 1. Spectral data from the two samples.