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

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). Copyright © 2010 John Wiley & Sons, Ltd

Chemical Functionalization of Diatom Silica Microparticles for Adsorption of Gold (III) Ions

“…The 23.4% C concentration indicated for the pristine DE is due to the surface contamination of adventitious carbon. 35 The atomic concentration of carbon increases from 23.4% to 26.7% and concentration of silicon from 17.4% to 19% corresponds to the introduction of the carbon chain with siliane froups from the MPTMS modification on the diatom surface. 36 The increase in atomic concentration of sulfur from 0 to 3.1% in the MPTMS-DE sample indicates a successful -SH surface functionalization.…”

Useful X-ray Photoelectron Spectroscopy-Based Chemical Tool: Differential Charging Studies of Complex Composite Materials

“…The effect results in spectral shifts toward higher binding energies and is prominent in nonconductive samples or parts of surface heterostructures. − In a sample of uniform composition, the shift can easily be compensated for by using an appropriate reference, but layered and otherwise heterogeneous materials will experience differential charging which cannot be corrected for in a simple manner. While the problem can be partially resolved using an electron flood gun, complete neutralization of the surface is difficult as attempts to replenish electrons can cause the buildup of negative charge or nonuniform charging of the sample. − When varied in a controlled manner, differential charging can be used to derive chemical and/or physical parameters of composite samples. − This approach, pioneered by Suzer and co-workers, has been effectively but not widely used to examine differential charging and the dynamics of charge transfer in complex composite samples.…”