Analysis of Fe nanoparticles using XPS measurements under d.c. or pulsed-voltage bias

Date
2010
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Source Title
Surface and Interface Analysis
Print ISSN
0142-2421
Electronic ISSN
1096-9918
Publisher
Volume
42
Issue
6-7
Pages
859 - 862
Language
English
Type
Article
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Abstract

The impact of solution exposure on the charging properties of oxide coatings on Fe metal-core oxide-shell nanoparticles has been examined by sample biasing during XPS measurements. The Fe nanoparticles were suspended in relatively unreactive acetone and analyzed after particles containing solutions were deposited on SiO2/Si or Au substrates. The particle and substrate combinations were subjected to ±10V d.c. or ±5V a.c., biasing in the form of square wave (SQW) pulses. The samples experienced variable degrees of charging for which low-energy electrons at ∼1eV, 20 μA and low-energy Ar+ ions were used to minimize it. Application of d.c. bias and/or SQW pulses significantly influences the extent of charging, which is utilized to gather additional analytical information about the sample under investigation. This approach allows separation of otherwise overlapping peaks. Accordingly, the O1s peaks of the silicon oxide substrate, the iron oxide nanoparticles, and that of the casting solvent can be separated from each other. Similarly, the C1s peak belonging to the solvent can be separated from that of the adventitious carbon. The charging shifts of the iron nanoparticles are strongly influenced by the solvent to which the particles were exposed. Hence, acetone exhibited the largest shift, water the smallest, and methanol in between. Dynamical measurements performed by application of the voltage stress in the form of SQW pulses provides information about the time constants of the processes involved, which leads us to postulate that these charging properties we probe in these systems stem mainly from ionic movement(s).

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Keywords
Casting from different solvents, Fe nanoparticles, XPS, Adventitious carbon, Charging property, Charging shifts, Different solvents, Fe metal, In-between, Ionic movement, Iron nanoparticles, Iron oxide nanoparticle, Low energy electrons, Low-energy Ar, Overlapping peaks, Oxide coating, Shell nanoparticles, Silicon oxide substrates, Square waves, Time constants, Voltage bias, Voltage stress, XPS measurements, Acetone, Ionization of liquids, Iron oxides, Methanol, Protective coatings, Silicon compounds, Silicon oxides, Solvents, Substrates, X ray photoelectron spectroscopy, Nanoparticles
Citation
Published Version (Please cite this version)