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Versailles Project on Advanced Materials and Standards Interlaboratory Study on Measuring the Thickness and Chemistry of Nanoparticle Coatings Using XPS and LEIS

Belsey, Natalie A.,Cant, David J. H.,Minelli, Caterina,Araujo, Joyce R.,Bock, Bernd,Brü,ner, Philipp,Castner, David G.,Ceccone, Giacomo,Counsell, Jonathan D. P.,Dietrich, Paul M.,Engelhard, Mark American Chemical Society 2016 The Journal of Physical Chemistry Part C Vol.120 No.42
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We report the results of a Versailles Project on Advanced Materials and Standards (VAMAS) interlaboratory study on the measurement of the shell thickness and chemistry of nanoparticle coatings. Peptide-coated gold particles were supplied to laboratories in two forms: a colloidal suspension in pure water and particles dried onto a silicon wafer. Participants prepared and analyzed these samples using either X-ray photoelectron spectroscopy (XPS) or low energy ion scattering (LEIS). Careful data analysis revealed some significant sources of discrepancy, particularly for XPS. Degradation during transportation, storage, or sample preparation resulted in a variability in thickness of 53%. The calculation method chosen by XPS participants contributed a variability of 67%. However, variability of 12% was achieved for the samples deposited using a single method and by choosing photoelectron peaks that were not adversely affected by instrumental transmission effects. The study identified a need for more consistency in instrumental transmission functions and relative sensitivity factors since this contributed a variability of 33%. The results from the LEIS participants were more consistent, with variability of less than 10% in thickness, and this is mostly due to a common method of data analysis. The calculation was performed using a model developed for uniform, flat films, and some participants employed a correction factor to account for the sample geometry, which appears warranted based upon a simulation of LEIS data from one of the participants and comparison to the XPS results.
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ToF-SIMS Analysis of Adsorbed Proteins: Principal Component Analysis of the Primary Ion Species Effect on the Protein Fragmentation Patterns

Muramoto, Shin,Graham, Daniel J.,Wagner, Matthew S.,Lee, Tae Geol,Moon, Dae Won,Castner, David G. American Chemical Society 2011 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.115 No.49
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In time-of-flight secondary ion mass spectrometry (ToF-SIMS), the choice of the primary ion used for analysis can influence the resulting mass spectrum. This is because different primary ion types can produce different fragmentation pathways. In this study, analysis of single-component protein monolayers were performed using monatomic, triatomic, and polyatomic primary ion sources. Eight primary ions (Cs+, Au+, Au3+, Bi+, Bi3+, Bi3++, C60+, and C60++) were used to examine the low mass (m/z < 200) fragmentation patterns from five different proteins (bovine serum albumin, bovine serum fibrinogen, bovine immunoglobulin G, and chicken egg white lysozyme) adsorbed onto mica surfaces. Principal component analysis (PCA) processing of the ToF-SIMS data showed that variation in peak intensity caused by the primary ions was greater than differences in protein composition. The spectra generated by Cs+, Au+, and Bi+ primary ions were similar, but the spectra generated by monatomic, triatomic, and polyatomic primary ions varied significantly. C60 primary ions increased fragmentation of the adsorbed proteins in the m/z < 200 region, resulting in more intense low m/z peaks. Thus, comparison of data obtained by one primary ion species with that obtained by another primary ion species should be done with caution. However, for the spectra generated using a given primary ion beam, discrimination between the spectra of different proteins followed similar trends. Therefore, a PCA model of proteins created with a given ion source should only be applied to data sets obtained using the same ion source. The type of information obtained from PCA depended on the peak set used. When only amino acid peaks were used, PCA was able to identify the relationship between proteins by their amino acid composition. When all peaks from m/z 12–200 were used, PCA separated proteins based on a ratio of C4H8N+ to K+ peak intensities. This ratio correlated with the thickness of the protein films, and Bi1+ primary ions produced the most surface sensitive spectra.Graphic Abstract <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2011/jpccck.2011.115.issue-49/jp208035x/production/images/medium/jp-2011-08035x_0002.gif'><A href='http://pubs.acs.org/doi/suppl/10.1021/jp208035x'>ACS Electronic Supporting Info</A>
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Organic Thin‐Film Transistors: Simultaneous Modification of Bottom‐Contact Electrode and Dielectric Surfaces for Organic Thin‐Film Transistors Through Single‐Component Spin‐Cast Monolayers (Adv. Funct. Mater. 8/2011)

Acton, Orb,Dubey, Manish,Weidner, Tobias,O’Malley, Kevin M.,Kim, Tae‐,Wook,Ting, Guy G.,Hutchins, Daniel,Baio, J. E.,Lovejoy, Tracy C.,Gage, Alexander H.,Castner, David G.,Ma, Hong,Jen, Alex K.& WILEY‐VCH Verlag 2011 Advanced functional materials Vol.21 No.8
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AbstractAn efficient process is developed by spin‐coating a single‐component, self‐assembled monolayer (SAM) to simultaneously modify the bottom‐contact electrode and dielectric surfaces of organic thin‐film transistors (OTFTs). This effi cient interface modifi cation is achieved using n‐alkyl phosphonic acid based SAMs to prime silver bottom‐contacts and hafnium oxide (HfO2) dielectrics in low‐voltage OTFTs. Surface characterization using near edge X‐ray absorption fi ne structure (NEXAFS) spectroscopy, X‐ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared (ATR‐FTIR) spectroscopy, atomic force microscopy (AFM), and spectroscopic ellipsometry suggest this process yields structurally well‐defi ned phosphonate SAMs on both metal and oxide surfaces. Rational selection of the alkyl length of the SAM leads to greatly enhanced performance for both n‐channel (C60) and p‐channel (pentacene) based OTFTs. Specifi cally, SAMs of n‐octylphos‐phonic acid (OPA) provide both low‐contact resistance at the bottom‐contact electrodes and excellent interfacial properties for compact semiconductor grain growth with high carrier mobilities. OTFTs based on OPA modifi ed silver electrode/HfO2 dielectric bottom‐contact structures can be operated using < 3V with low contact resistance (down to 700 Ohm‐cm), low subthreshold swing (as low as 75 mV dec−1), high on/off current ratios of 107, and charge carrier mobilities as high as 4.6 and 0.8 cm2 V−1 s−1, for C60 and pentacene, respectively. These results demonstrate that this is a simple and efficient process for improving the performance of bottom‐contact OTFTs.

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