MULTI-MODE ION SOURCE continued a
Understanding the production of the amino acid multi-layer substrate is an important step in the
development of a working sensor.
Figure 6 – MAGCIS cluster profile of (a) damaged and (b) intact amino acid multi-layer.
the C1s spectrum. During profiling, the integrity of the amino acid can be monitored by the presence of what is known as a “shake-up” feature, characteristic in this case of the presence of the aromatic ring in both molecules. Any sputtering damage to the sample will cause this feature to disappear, as shown in Figure 5. If this feature disappears when using the cluster sputtering source, then it is due to the sample and not the experimental method, unlike monatomic ion bombardment.
Figure 6 depicts the depth profiles from two samples. The first shows that the top Phe layer has been damaged or incorrectly deposited, and is much thinner than expected. Their oxygen signatures allow the three Tyr layers to be identified easily, and the layers appear to be deposited correctly. The second profile shows that the expected structure was deposited. Cluster ion profiling’s ability to analyze these kinds of materials makes it possible to fully comprehend the structures being made, and potentially make increasingly complex modifications to customize devices for specific uses.
Summary Since their recent introduction to surface analysis, gas cluster ion sources
Figure 5 – C1s spectra from monatomic Ar+ showing damage to the molecule.
profile of amino acid layers
the optical properties of the sensor when the target molecules attach to the binding surface of the device. Understanding the production of the amino acid multi-layer substrate is an important step in the development of a working sensor.
Alternating layers of two amino acids—phenylalanine (Phe) and tyrosine (Tyr)—make up the multi-layer (Figure 4). These layers are made by thermal evaporation of the solid materials onto a silicon substrate. The two mol- ecules are similar, differing in the additional hydroxyl (–OH) only. This subtle change is easy to detect by XPS, as shown in the reference spectra of the two samples. The presence of the Tyr layers can be observed by a change in the oxygen quantification and in the intensities of the components of
AMERICAN LABORATORY 16
have become a standard addition to XPS systems. Their ability to remove material from the surface while preserving the underlying chemistry is unmatched by previously available technology and has permitted the analysis of samples that could not be analyzed successfully. Combining this with a more traditional monatomic ion source like the Thermo Scientific MAGCIS system enables investigation of the widest possible range of materials.
Tim Nunney is surface analysis product manager, Thermo Fisher Scientific, Birches Industrial Estate, East Grinstead RH19 1UB, U.K.; tel.: +44 (0)1342 310290; e-mail:
tim.nunney@
thermofisher.com;
www.xps-simplified.com. The author thanks Dietrich R.T. Zahn, Daniel Lehmann and Iulia Korodi from Chemnitz University of Technology, Germany, for use of the organic FET sample, and Jean-Jacques Pireaux and Pierre Louette from Laboratoire Inter- disciplinaire de Spectroscopie Electronique, Facultés Universitaires Notre Dame de la Paix, Namur, Belgium, for the use of the biosensor multi-layer sample.
MARCH 2016 b
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60